Debian Policy Manual
********************

This manual describes the policy requirements for the Debian
distribution. This includes the structure and contents of the Debian
archive and several design issues of the operating system, as well as
technical requirements that each package must satisfy to be included
in the distribution.

This is Debian Policy version 4.7.4.1, released on 2026-03-31.

* 1. About this manual

  * 1.1. Scope

  * 1.2. New versions of this document

  * 1.3. Authors and Maintainers

    * 1.3.1. Early history

    * 1.3.2. Current process

    * 1.3.3. Improvements

  * 1.4. Related documents

  * 1.5. Definitions

  * 1.6. Translations

* 2. The Debian Archive

  * 2.1. The Debian Free Software Guidelines

  * 2.2. Archive areas

    * 2.2.1. The main archive area

    * 2.2.2. The non-free-firmware archive area

    * 2.2.3. The contrib archive area

    * 2.2.4. The non-free archive area

  * 2.3. Copyright considerations

  * 2.4. Sections

  * 2.5. Priorities

* 3. Binary packages

  * 3.1. The package name

    * 3.1.1. Packages with potentially offensive content

  * 3.2. The version of a package

    * 3.2.1. Version numbers based on dates

    * 3.2.2. Uniqueness of version numbers

  * 3.3. The maintainer of a package

  * 3.4. The description of a package

    * 3.4.1. The single line synopsis

    * 3.4.2. The extended description

  * 3.5. Dependencies

  * 3.6. Virtual packages

  * 3.7. Base system

  * 3.8. Essential packages

  * 3.9. Maintainer Scripts

    * 3.9.1. Prompting in maintainer scripts

* 4. Source packages

  * 4.1. Standards conformance

  * 4.2. Package relationships

  * 4.3. Changes to the upstream sources

  * 4.4. Debian changelog: "debian/changelog"

  * 4.5. Copyright: "debian/copyright"

  * 4.6. Error trapping in makefiles

  * 4.7. Time Stamps

  * 4.8. Restrictions on objects in source packages

  * 4.9. Main building script: "debian/rules"

    * 4.9.1. "debian/rules" and "DEB_BUILD_OPTIONS"

    * 4.9.2. "debian/rules" and "DEB_BUILD_PROFILES"

    * 4.9.3. "debian/rules" and "Rules-Requires-Root"

  * 4.10. Variable substitutions: "debian/substvars"

  * 4.11. Upstream source location: "debian/watch"

  * 4.12. Generated files list: "debian/files"

  * 4.13. Embedded code copies

  * 4.14. Source package handling: "debian/README.source"

  * 4.15. Reproducibility

  * 4.16. Missing sources: "debian/missing-sources"

  * 4.17. Vendor-specific patch series

* 5. Control files and their fields

  * 5.1. Syntax of control files

  * 5.2. Debian source package template control files --
    "debian/control"

  * 5.3. Debian binary package control files -- "DEBIAN/control"

  * 5.4. Debian source package control files -- ".dsc"

  * 5.5. Debian upload changes control files -- ".changes"

  * 5.6. List of fields

    * 5.6.1. "Source"

    * 5.6.2. "Maintainer"

    * 5.6.3. "Uploaders"

    * 5.6.4. "Changed-By"

    * 5.6.5. "Section"

    * 5.6.6. "Priority"

    * 5.6.7. "Package"

    * 5.6.8. "Architecture"

    * 5.6.9. "Essential"

    * 5.6.10. Package interrelationship fields: "Depends", "Pre-
      Depends", "Recommends", "Suggests", "Breaks", "Conflicts",
      "Provides", "Replaces", "Enhances"

    * 5.6.11. "Standards-Version"

    * 5.6.12. "Version"

      * 5.6.12.1. Epochs should be used sparingly

      * 5.6.12.2. Special version conventions

    * 5.6.13. "Description"

    * 5.6.14. "Distribution"

    * 5.6.15. "Date"

    * 5.6.16. "Format"

    * 5.6.17. "Urgency"

    * 5.6.18. "Changes"

    * 5.6.19. "Binary"

    * 5.6.20. "Installed-Size"

    * 5.6.21. "Files"

    * 5.6.22. "Closes"

    * 5.6.23. "Homepage"

    * 5.6.24. "Checksums-Sha1" and "Checksums-Sha256"

    * 5.6.25. "DM-Upload-Allowed"

    * 5.6.26. Version Control System (VCS) fields

    * 5.6.27. "Package-List"

    * 5.6.28. "Package-Type"

    * 5.6.29. "Dgit"

    * 5.6.30. "Testsuite"

    * 5.6.31. "Rules-Requires-Root"

      * 5.6.31.1. Remarks

      * 5.6.31.2. Definition of the keywords

      * 5.6.31.3. Provided keywords

    * 5.6.32. "Git-Tag-Tagger"

    * 5.6.33. "Git-Tag-Info"

    * 5.6.34. "Multi-Arch"

      * 5.6.34.1. "Multi-Arch: no"

      * 5.6.34.2. "Multi-Arch: foreign"

      * 5.6.34.3. "Multi-Arch: same"

      * 5.6.34.4. "Multi-Arch: allowed"

    * 5.6.35. "Build-Profiles"

  * 5.7. User-defined fields

  * 5.8. Obsolete fields

    * 5.8.1. "DM-Upload-Allowed"

* 6. Package maintainer scripts and installation procedure

  * 6.1. Introduction to package maintainer scripts

  * 6.2. Maintainer scripts idempotency

  * 6.3. Controlling terminal for maintainer scripts

  * 6.4. Exit status

  * 6.5. Summary of ways maintainer scripts are called

  * 6.6. Details of unpack phase of installation or upgrade

  * 6.7. Details of configuration

  * 6.8. Details of removal and/or configuration purging

* 7. Declaring relationships between packages

  * 7.1. Syntax of relationship fields

    * 7.1.1. Restrictions

      * 7.1.1.1. Architecture restrictions

      * 7.1.1.2. Build profile restriction formulas

  * 7.2. Binary Dependencies - "Depends", "Recommends", "Suggests",
    "Enhances", "Pre-Depends"

  * 7.3. Packages which break other packages - "Breaks"

  * 7.4. Conflicting binary packages - "Conflicts"

  * 7.5. Virtual packages - "Provides"

  * 7.6. Overwriting files and replacing packages - "Replaces"

    * 7.6.1. Overwriting files in other packages

    * 7.6.2. Replacing whole packages, forcing their removal

  * 7.7. Relationships between source and binary packages - "Build-
    Depends", "Build-Depends-Indep", "Build-Depends-Arch", "Build-
    Conflicts", "Build-Conflicts-Indep", "Build-Conflicts-Arch"

  * 7.8. Additional source packages used to build the binary - "Built-
    Using"

* 8. Shared libraries

  * 8.1. Run-time shared libraries

    * 8.1.1. "ldconfig"

  * 8.2. Shared library support files

  * 8.3. Static libraries

  * 8.4. Development files

  * 8.5. Dependencies between the packages of the same library

  * 8.6. Dependencies between the library and other packages

    * 8.6.1. Generating dependencies on shared libraries

    * 8.6.2. Shared library ABI changes

    * 8.6.3. The "symbols" system

      * 8.6.3.1. The "symbols" files present on the system

      * 8.6.3.2. The "symbols" File Format

      * 8.6.3.3. Providing a "symbols" file

    * 8.6.4. The "shlibs" system

      * 8.6.4.1. The "shlibs" files present on the system

      * 8.6.4.2. The "shlibs" File Format

      * 8.6.4.3. Providing a "shlibs" file

* 9. The Operating System

  * 9.1. File system hierarchy

    * 9.1.1. File System Structure

    * 9.1.2. Site-specific programs

    * 9.1.3. The system-wide mail directory

    * 9.1.4. "/run" and "/run/lock"

  * 9.2. Users and groups

    * 9.2.1. Introduction

    * 9.2.2. UID and GID classes

    * 9.2.3. Non-existent home directories

  * 9.3. Starting system services

    * 9.3.1. Introduction

    * 9.3.2. Writing the scripts

    * 9.3.3. Interfacing with init systems

      * 9.3.3.1. Managing the links

      * 9.3.3.2. Running init scripts

    * 9.3.4. Boot-time initialization

    * 9.3.5. Example

  * 9.4. Console messages from "init.d" scripts

  * 9.5. Cron jobs

    * 9.5.1. Cron job file names

  * 9.6. Menus

  * 9.7. Multimedia handlers

    * 9.7.1. Registration of media type handlers with desktop entries

    * 9.7.2. Registration of media type handlers with mailcap entries

    * 9.7.3. Providing media types to files

  * 9.8. Keyboard configuration

  * 9.9. Environment variables

  * 9.10. Registering Documents using doc-base

  * 9.11. Alternate init systems

    * 9.11.1. Event-based boot with upstart

  * 9.12. Signaling that a reboot is required

* 10. Files

  * 10.1. Binaries

  * 10.2. Libraries

  * 10.3. Shared libraries

  * 10.4. Scripts

  * 10.5. Symbolic links

  * 10.6. Device files

  * 10.7. Configuration files

    * 10.7.1. Definitions

    * 10.7.2. Location

    * 10.7.3. Behavior

    * 10.7.4. Sharing configuration files

    * 10.7.5. User configuration files ("dotfiles")

  * 10.8. Log files

  * 10.9. Locale files

  * 10.10. Permissions and owners

    * 10.10.1. The use of "dpkg-statoverride"

  * 10.11. File names

* 11. Customized programs

  * 11.1. Architecture specification strings

    * 11.1.1. Architecture wildcards

  * 11.2. Daemons

  * 11.3. Using pseudo-ttys and modifying wtmp, utmp and lastlog

  * 11.4. Editors and pagers

  * 11.5. Web servers and applications

  * 11.6. Mail transport, delivery and user agents

  * 11.7. News system configuration

  * 11.8. Programs for the X Window System

    * 11.8.1. Providing X support and package priorities

    * 11.8.2. Packages providing an X server

    * 11.8.3. Packages providing a terminal emulator

    * 11.8.4. Packages providing a window manager

    * 11.8.5. Packages providing fonts

    * 11.8.6. Application defaults files

    * 11.8.7. Installation directory issues

  * 11.9. Perl programs and modules

  * 11.10. Emacs lisp programs

  * 11.11. Games

* 12. Documentation

  * 12.1. Manual pages

  * 12.2. Info documents

  * 12.3. Additional documentation

  * 12.4. Preferred documentation formats

  * 12.5. Copyright information

    * 12.5.1. Machine-readable copyright information

  * 12.6. Examples

  * 12.7. Changelog files and release notes


Appendices
^^^^^^^^^^

* 1. Introduction and scope of these appendices

* 2. Binary packages (from old Packaging Manual)

  * 2.1. Creating package files - "dpkg-deb"

  * 2.2. Binary package metadata files

  * 2.3. The binary package control file: "control"

  * 2.4. Time Stamps

* 3. Source packages (from old Packaging Manual)

  * 3.1. Tools for processing source packages

    * 3.1.1. "dpkg-source" - packs and unpacks Debian source packages

    * 3.1.2. "dpkg-buildpackage" - overall package-building control
      script

    * 3.1.3. "dpkg-gencontrol" - generates binary package control
      files

    * 3.1.4. "dpkg-shlibdeps" - calculates shared library dependencies

    * 3.1.5. "dpkg-distaddfile" - adds a file to "debian/files"

    * 3.1.6. "dpkg-genchanges" - generates a ".changes" upload control
      file

    * 3.1.7. "dpkg-parsechangelog" - produces parsed representation of
      a changelog

    * 3.1.8. "dpkg-architecture" - information about the build and
      host system

  * 3.2. The Debian package source tree

    * 3.2.1. "debian/rules" - the main building script

    * 3.2.2. "debian/substvars" and variable substitutions

    * 3.2.3. "debian/files"

    * 3.2.4. "debian/tmp"

  * 3.3. Source packages as archives

  * 3.4. Unpacking a Debian source package without "dpkg-source"

    * 3.4.1. Restrictions on objects in source packages

* 4. Control files and their fields (from old Packaging Manual)

  * 4.1. Syntax of control files

  * 4.2. List of fields

    * 4.2.1. "Filename"

    * 4.2.2. "Size" and "MD5sum"

    * 4.2.3. "Status"

    * 4.2.4. "Config-Version"

    * 4.2.5. "Conffiles"

    * 4.2.6. Obsolete fields

* 5. Configuration file handling (from old Packaging Manual)

  * 5.1. Automatic handling of configuration files by "dpkg"

  * 5.2. Fully-featured maintainer script configuration handling

* 6. Alternative versions of an interface - "update-alternatives"
  (from old Packaging Manual)

* 7. Diversions - overriding a package's version of a file (from old
  Packaging Manual)

* 8. Debian Policy changes process

  * 8.1. Introduction

  * 8.2. Change Goals

  * 8.3. Current Process

    * 8.3.1. State A: More information required

    * 8.3.2. State B: Discussion

    * 8.3.3. State C: Proposal

    * 8.3.4. State D: Wording proposed

    * 8.3.5. State E: Seconded

    * 8.3.6. State F: Accepted

    * 8.3.7. State G: Reject

  * 8.4. Other Tags

* 9. Maintainer script flowcharts

* 10. Upgrading checklist

  * 10.1. About the checklist

  * 10.2. Version 4.7.4

  * 10.3. Version 4.7.3

  * 10.4. Version 4.7.2

  * 10.5. Version 4.7.1

  * 10.6. Version 4.7.0

  * 10.7. Version 4.6.2

  * 10.8. Version 4.6.1

  * 10.9. Version 4.6.0

  * 10.10. Version 4.5.1

  * 10.11. Version 4.5.0

  * 10.12. Version 4.4.1

  * 10.13. Version 4.4.0

  * 10.14. Version 4.3.0

  * 10.15. Version 4.2.1

  * 10.16. Version 4.2.0

  * 10.17. Version 4.1.5

  * 10.18. Version 4.1.4

  * 10.19. Version 4.1.3

  * 10.20. Version 4.1.2

  * 10.21. Version 4.1.1

  * 10.22. Version 4.1.0

  * 10.23. Version 4.0.1

  * 10.24. Version 4.0.0

  * 10.25. Version 3.9.8

  * 10.26. Version 3.9.7

  * 10.27. Version 3.9.6

  * 10.28. Version 3.9.5

  * 10.29. Version 3.9.4

  * 10.30. Version 3.9.3

  * 10.31. Version 3.9.2

  * 10.32. Version 3.9.1

  * 10.33. Version 3.9.0

  * 10.34. Version 3.8.4

  * 10.35. Version 3.8.3

  * 10.36. Version 3.8.2

  * 10.37. Version 3.8.1

  * 10.38. Version 3.8.0

  * 10.39. Version 3.7.3

  * 10.40. Version 3.7.2.2

  * 10.41. Version 3.7.2

  * 10.42. Version 3.7.1

  * 10.43. Version 3.7.0

  * 10.44. Version 3.6.2

  * 10.45. Version 3.6.1

  * 10.46. Version 3.6.0

  * 10.47. Version 3.5.10

  * 10.48. Version 3.5.9

  * 10.49. Version 3.5.8

  * 10.50. Version 3.5.7

  * 10.51. Version 3.5.6

  * 10.52. Version 3.5.5

  * 10.53. Version 3.5.4

  * 10.54. Version 3.5.3

  * 10.55. Version 3.5.2

  * 10.56. Version 3.5.1

  * 10.57. Version 3.5.0

  * 10.58. Version 3.2.1.1

  * 10.59. Version 3.2.1

  * 10.60. Version 3.2.0

  * 10.61. Version 3.1.1

  * 10.62. Version 3.1.0

  * 10.63. Version 3.0.1

  * 10.64. Version 3.0.0

  * 10.65. Version 2.5.0

  * 10.66. Version 2.4.1

  * 10.67. Version 2.4.0

  * 10.68. Version 2.3.0

  * 10.69. Version 2.2.0

  * 10.70. Version 2.1.3

  * 10.71. Version 2.1.2

  * 10.72. Version 2.1.1

  * 10.73. Version 2.1.0

* 11. License



1. About this manual
********************


1.1. Scope
==========

This manual describes the policy requirements for the Debian
distribution. This includes the structure and contents of the Debian
archive and several design issues of the operating system, as well as
technical requirements that each package must satisfy to be included
in the distribution.

This manual also describes Debian policy as it relates to creating
Debian packages. It is not a tutorial on how to build packages, nor is
it exhaustive where it comes to describing the behavior of the
packaging system. Instead, this manual attempts to define the
interface to the package management system with which the developers
must be conversant.  [1]

This manual cannot and does not prohibit every possible bug or
undesirable behaviour.  The fact that something is not prohibited by
Debian policy does not mean that it is not a bug, let alone that it is
desirable.  Questions not covered by policy should be evaluated on
their merits.

The footnotes present in this manual are merely informative, and are
not part of Debian policy itself.

The appendices to this manual are not necessarily normative, either.
Please see Introduction and scope of these appendices for more
information.

In the normative part of this manual, the following terms are used to
describe the importance of each statement:  [2]

* The terms *must* and *must not*, and the adjectives *required* and
  *prohibited*, denote strong requirements. Packages that do not
  conform to these requirements will generally not be considered
  acceptable for the Debian distribution. These statements correspond
  to the *critical*, *grave*, and *serious* bug severities (normally
  serious). They are collectively called *Policy requirements*.

* The terms *should* and *should not*, and the adjective
  *recommended*, denote best practices. Non-conformance with these
  guidelines will generally be considered a bug, but will not
  necessarily render a package unsuitable for distribution. These
  statements correspond to bug severities of *important*, *normal*,
  and *minor*. They are collectively called *Policy recommendations*.

* The adjectives *encouraged* and *discouraged* denote places where
  Policy offers advice to maintainers, but maintainers are free to
  follow or not follow that advice. Non-conformance with this advice
  is normally not considered a bug; if a bug seems worthwhile,
  normally it would have a severity of *wishlist*. These statements
  are collectively called *Policy advice*.

* The term *may* and the adjective *optional* are used to clarify
  cases where it may otherwise appear that Policy is specifying a
  requirement or recommendation. In those cases, these words describe
  decisions that are truly optional and at the maintainer's
  discretion.

The Release Team can, at their discretion, downgrade a Policy
requirement to a Policy recommendation for a given release of the
Debian distribution. This may be done for only a specific package or
for the archive as a whole. This provision is intended to provide
flexibility to balance the quality standards of the distribution
against the release schedule and the importance of making a stable
release.

Much of the information presented in this manual will be useful even
when building a package which is to be distributed in some other way
or is intended for local use only.

udebs (stripped-down binary packages used by the Debian Installer) and
source packages that produce only udebs do not comply with all of the
requirements discussed here. See the Debian Installer internals manual
for more information about them.

[1] Informally, the criteria used for inclusion is that the material
    meet one of the following requirements:

    Standard interfaces
       The material presented represents an interface to the packaging
       system that is mandated for use, and is used by, a significant
       number of packages, and therefore should not be changed without
       peer review. Package maintainers can then rely on this
       interface not changing, and the package management software
       authors need to ensure compatibility with this interface
       definition. (Control file and changelog file formats are
       examples.)

    Chosen Convention
       If there are a number of technically viable choices that can be
       made, but one needs to select one of these options for inter-
       operability. The version number format is one example.

    Please note that these are not mutually exclusive; selected
    conventions often become parts of standard interfaces.

[2] Compare RFC 2119. Note, however, that these words are used in a
    different way in this document.


1.2. New versions of this document
==================================

This manual is distributed via the Debian package debian-policy.

The current version of this document is also available from the Debian
web mirrors at https://www.debian.org/doc/debian-policy/. Also
available from the same directory are several other formats:
policy.epub, policy.txt and policy.pdf. Included in both the same
directory and in the debian-policy package is a standalone copy of
Upgrading checklist, which indicates policy changes between versions
of this document.


1.3. Authors and Maintainers
============================


1.3.1. Early history
--------------------

Originally called "Debian GNU/Linux Policy Manual", this manual was
initially written in 1996 by Ian Jackson. It was revised on November
27th, 1996 by David A. Morris. Christian Schwarz added new sections on
March 15th, 1997, and reworked/restructured it in April-July 1997.
Christoph Lameter contributed the "Web Standard". Julian Gilbey
largely restructured it in 2001.  Since September 1998, changes to the
contents of this document have been co-ordinated by means of the
debian-policy mailing list


1.3.2. Current process
----------------------

The Policy Editors are DPL delegates with responsibility for the
contents of this document (see the Debian Constitution for the meaning
of "DPL delegate").  However, the Policy Editors further delegate
their editorial power to a process of establishing project member
consensus on the debian-policy mailing list, as described in Debian
Policy changes process.  The current Policy Editors are:

1. Russ Allbery

2. Sean Whitton


1.3.3. Improvements
-------------------

While the authors of this document have tried hard to avoid typos and
other errors, these do still occur. If you discover an error in this
manual or if you want to give any comments, suggestions, or criticisms
please send an email to the Debian Policy Mailing List, debian-
policy@lists.debian.org, or submit a bug report against the "debian-
policy" package.

Please do not try to reach the individual authors or maintainers of
the Policy Manual regarding changes to the Policy.

New techniques and functionality are generally implemented in the
Debian archive (long) before they are detailed in this document.  This
is not considered to be a problem: there is a consensus in the Debian
Project that the task of keeping this document up-to-date should never
block making improvements to Debian.  Nevertheless, it is better to
submit patches to this document sooner rather than later.  This
reduces the amount of work that is needed on the part of others to get
themselves up-to-speed on new best practices.


1.4. Related documents
======================

There are several other documents other than this Policy Manual that
are necessary to fully understand some Debian policies and procedures.

The external "sub-policy" documents are referred to in:

* File System Structure

* Virtual packages

* Menus

* Perl programs and modules

* Prompting in maintainer scripts

* Emacs lisp programs

In addition to those, which carry the weight of policy, there is the
Debian Developer's Reference. This document describes procedures and
resources for Debian developers, but it is *not* normative; rather, it
includes things that don't belong in the Policy, such as best
practices for developers.

The Developer's Reference is available in the developers-reference
package. It's also available from the Debian web mirrors at
https://www.debian.org/doc/developers-reference/.

Finally, a specification for machine-readable copyright files is
maintained as part of the debian-policy package using the same
procedure as the other policy documents. Use of this format is
optional.


1.5. Definitions
================

The following terms are used in this Policy Manual:

ASCII
   The character encoding specified by ANSI X3.4-1986 and its
   predecessor standards, referred to in MIME as US-ASCII, and
   corresponding to an encoding in eight bits per character of the
   first 128 Unicode characters, with the eighth bit always zero.

upstream
   The source of software that is being packaged, or the portion of a
   software package that originates from outside of Debian.  For
   example, suppose Alice writes and releases a free software package,
   and then Bob creates a Debian package of that software package.
   Alice is the *upstream maintainer* (sometimes abbreviated as
   *upstream*) of the package, Alice's releases are the *upstream
   releases*, and the version number she puts on a release is the
   *upstream version*.  Bob may make Debian-specific modifications to
   the package, and then later send those modifications *upstream* to
   be incorporated in Alice's releases.

   The packager and upstream developer may be the same person.  For
   example, Alice may choose to package her own software for Debian.
   However, this manual still distinguishes between the role of
   upstream and the role of Debian packager, even when the same person
   is filling both of those roles, since they have some implications
   for the details of packaging.

UTF-8
   The transformation format (sometimes called encoding) of Unicode
   defined by RFC 3629. UTF-8 has the useful property of having ASCII
   as a subset, so any text encoded in ASCII is trivially also valid
   UTF-8.


1.6. Translations
=================

When translations of this document into languages other than English
disagree with the English text, the English text takes precedence.



2. The Debian Archive
*********************

The Debian system is maintained and distributed as a collection of
*packages*. Since there are so many of them (currently well over
15000), they are split into *sections* and given *priorities* to
simplify the handling of them.

The effort of the Debian project is to build a free operating system,
but not every package we want to make accessible is *free* in our
sense (see the Debian Free Software Guidelines, below), or may be
imported/exported without restrictions. Thus, the archive is split
into areas [1] based on their licenses and other restrictions.

The aims of this are:

* to allow us to make as much software available as we can

* to allow us to encourage everyone to write free software, and

* to allow us to make it easy for people to produce CD-ROMs of our
  system without violating any licenses, import/export restrictions,
  or any other laws.

The *main* archive area forms the *Debian distribution*.

Packages in the other archive areas ("non-free-firmware", "contrib",
"non-free") are not considered to be part of the Debian distribution,
although we support their use and provide infrastructure for them
(such as our bug-tracking system and mailing lists). This Debian
Policy Manual applies to these packages as well.

[1] The Debian archive software uses the term "component" internally
    and in the Release file format to refer to the division of an
    archive. The Debian Social Contract simply refers to "areas." This
    document uses terminology similar to the Social Contract.


2.1. The Debian Free Software Guidelines
========================================

The Debian Free Software Guidelines (DFSG) form our definition of
"free software". These are:

1. Free Redistribution
      The license of a Debian component may not restrict any party
      from selling or giving away the software as a component of an
      aggregate software distribution containing programs from several
      different sources. The license may not require a royalty or
      other fee for such sale.

2. Source Code
      The program must include source code, and must allow
      distribution in source code as well as compiled form.

3. Derived Works
      The license must allow modifications and derived works, and must
      allow them to be distributed under the same terms as the license
      of the original software.

4. Integrity of The Author's Source Code
      The license may restrict source-code from being distributed in
      modified form *only* if the license allows the distribution of
      "patch files" with the source code for the purpose of modifying
      the program at build time. The license must explicitly permit
      distribution of software built from modified source code. The
      license may require derived works to carry a different name or
      version number from the original software. (This is a
      compromise. The Debian Project encourages all authors to not
      restrict any files, source or binary, from being modified.)

5. No Discrimination Against Persons or Groups
      The license must not discriminate against any person or group of
      persons.

6. No Discrimination Against Fields of Endeavor
      The license must not restrict anyone from making use of the
      program in a specific field of endeavor. For example, it may not
      restrict the program from being used in a business, or from
      being used for genetic research.

7. Distribution of License
      The rights attached to the program must apply to all to whom the
      program is redistributed without the need for execution of an
      additional license by those parties.

8. License Must Not Be Specific to Debian
      The rights attached to the program must not depend on the
      program's being part of a Debian system. If the program is
      extracted from Debian and used or distributed without Debian but
      otherwise within the terms of the program's license, all parties
      to whom the program is redistributed must have the same rights
      as those that are granted in conjunction with the Debian system.

9. License Must Not Contaminate Other Software
      The license must not place restrictions on other software that
      is distributed along with the licensed software. For example,
      the license must not insist that all other programs distributed
      on the same medium must be free software.

10. Example Licenses
       The "GPL," "BSD," and "Artistic" licenses are examples of
       licenses that we consider *free*.


2.2. Archive areas
==================


2.2.1. The main archive area
----------------------------

The *main* archive area comprises the Debian distribution. Only the
packages in this area are considered part of the distribution. None of
the packages in the *main* archive area require software outside of
that area to function. Anyone may use, share, modify and redistribute
the packages in this archive area freely [2].

Every package in *main* must comply with the DFSG (Debian Free
Software Guidelines).  [3]

In addition, the packages in *main*

* must not require or recommend a package outside of *main* for
  compilation or execution (thus, the package must not declare a "Pre-
  Depends", "Depends", "Recommends", "Build-Depends", "Build-Depends-
  Indep", or "Build-Depends-Arch" relationship on a non-*main* package
  unless that package is only listed as a non-default alternative for
  a package in *main*),

* must not be so buggy that we refuse to support them, and

* must meet all policy requirements presented in this manual.

If a source package is in the *main* archive area, then at least one
of its binary packages must be in the *main* archive area, and each of
the remaining packages must be in either the *main* or *contrib*
archive area. Each binary package's archive area is indicated by its
"Section" field: see Sections.

Source packages in *main* with a mixture of *main* and *contrib*
binary packages are more complex for archive tooling to handle, and
therefore should be limited to situations where it would be
inconvenient to split the source package. If it is straightforward to
split the source package into a *main* part and a *contrib* part that
are built separately, then those parts should be represented as
separate source packages.

When a *main* source package has a mixture of *main* and *contrib*
binary packages, the source package and the *main* binary packages
must follow the requirements for *main* packages, but the *contrib*
binary packages may follow the weaker requirements for *contrib*
packages. In particular, source packages in *main* must not have build
dependencies outside *main*, but the *contrib* binary packages may
have runtime dependencies outside *main*.

[2] See What Does Free Mean? for more about what we mean by free
    software.

[3] Debian's FTP Masters publish a REJECT-FAQ which details the
    project's current working interpretation of the DFSG.


2.2.2. The non-free-firmware archive area
-----------------------------------------

The *non-free-firmware* archive area contains packages providing
firmware needed to initialize, use or keep updated hardware required
by our users, typically necessary for important functions to be
available (i.e. wireless network connectivity) or for fixing security
defects in hardware (i.e. CPU microcode updates). Packages in this
archive may not comply with all of the policy requirements in this
manual due to lack of source code availability, restrictions on
modification or other limitations.

Packages in *non-free-firmware*

* must not be so buggy that we refuse to support them, and

* must meet all policy requirements presented in this manual that it
  is possible for them to meet. [4]


2.2.3. The contrib archive area
-------------------------------

The *contrib* archive area contains supplemental packages intended to
work with the Debian distribution, but which require software outside
of the distribution to either build or function.

Every package in *contrib* must comply with the DFSG.

In addition, the packages in *contrib*

* must not be so buggy that we refuse to support them, and

* must meet all policy requirements presented in this manual.

Examples of packages which would be included in *contrib* are:

* free packages which require *contrib*, *non-free* packages or
  packages which are not in our archive at all for compilation or
  execution, and

* wrapper packages or other sorts of free accessories for non-free
  programs.

If a source package is in the *contrib* archive area, then each of the
binary packages that it produces must also be in the *contrib* archive
area.


2.2.4. The non-free archive area
--------------------------------

The *non-free* archive area contains supplemental packages intended to
work with the Debian distribution that do not comply with the DFSG or
have other problems that make their distribution problematic. They may
not comply with all of the policy requirements in this manual due to
restrictions on modifications or other limitations.

Packages must be placed in *non-free* if they are not compliant with
the DFSG or are encumbered by patents or other legal issues that make
their distribution problematic.

In addition, the packages in *non-free*

* must not be so buggy that we refuse to support them, and

* must meet all policy requirements presented in this manual that it
  is possible for them to meet.  [4]

If a source package is in the *non-free* archive area, then each of
the binary packages that it produces must also be in the *non-free*
archive area.

[4] It is possible that there are policy requirements which the
    package is unable to meet, for example, if the source is
    unavailable. These situations will need to be handled on a case-
    by-case basis.


2.3. Copyright considerations
=============================

Every package must be accompanied by a verbatim copy of its
distribution license(s) in the file
"/usr/share/doc/PACKAGE/copyright".

The copyright information for files in a package must be copied
verbatim into "/usr/share/doc/PACKAGE/copyright", when all of the
following hold:

1. the distribution license for those files requires that copyright
   information be included in all copies and/or binary distributions;

2. the files are shipped in the binary package, either in source or
   compiled form; and

3. the form in which the files are present in the binary package does
   not include a plain text version of their copyright notices.

Thus, the copyright information for files in the source package which
are only part of its build process, such as autotools files, need not
be included in "/usr/share/doc/PACKAGE/copyright", because those files
do not get installed into the binary package.  Similarly, plain text
files which include their own copyright information and are installed
into the binary package unmodified need not have that copyright
information copied into "/usr/share/doc/PACKAGE/copyright"

However, the copyright notices for any files which are compiled into
the object code shipped in the binary package must all be included in
"/usr/share/doc/PACKAGE/copyright" when the license requires that
copyright information be included in all copies and/or binary
distributions, as most do.  [5]

See Copyright information for further details.

We reserve the right to restrict files from being included anywhere in
our archives if

* their use or distribution would break a law,

* there is an ethical conflict in their distribution or use,

* we would have to sign a license for them, or

* their distribution would conflict with other project policies.

Programs whose authors encourage the user to make donations are fine
for the main distribution, provided that the authors do not claim that
not donating is immoral, unethical, illegal or something similar; in
such a case they must go in *non-free*.

Packages whose copyright permission notices (or patent problems) do
not even allow redistribution of binaries only, and where no special
permission has been obtained, must not be placed on the Debian FTP
site and its mirrors at all.

Note that under international copyright law (this applies in the
United States, too), *no* distribution or modification of a work is
allowed without an explicit notice saying so. Therefore a program
without a copyright notice *is* copyrighted and you may not do
anything to it without risking being sued! Likewise if a program has a
copyright notice but no statement saying what is permitted then
nothing is permitted.

Many authors are unaware of the problems that restrictive copyrights
(or lack of copyright notices) can cause for the users of their
supposedly-free software. It is often worthwhile contacting such
authors diplomatically to ask them to modify their license terms.
However, this can be a politically difficult thing to do and you
should ask for advice on the "debian-legal" mailing list first, as
explained below.

When in doubt about a copyright, send mail to debian-
legal@lists.debian.org. Be prepared to provide us with the copyright
statement. Software covered by the GPL, public domain software and
BSD-like copyrights are safe; be wary of the phrases "commercial use
prohibited" and "distribution restricted".

[5] Licenses that are not thought to require the copying of all
    copyright notices into Debian's copyright file include Apache-2.0
    and the Boost Software License, version 1.0.  Final determination
    as to whether a package's copyright file is sufficient lies with
    the FTP team.

    To help find copyright notices you need to copy, you might try
    "grep --color=always -Eir '(copyright|©)' * | less -R"


2.4. Sections
=============

The packages in the archive areas *main*, *non-free-firmware*,
*contrib* and *non-free* are grouped further into *sections* to
simplify handling.

The archive area and section for each package should be specified in
the package's "Section" control field (see Section). However, the
maintainer of the Debian archive may override this selection to ensure
the consistency of the Debian distribution. The "Section" field should
be of the form:

* *section* if the package is in the *main* archive area,

* *area/section* if the package is in the *non-free-firmware*,
  *contrib* or *non-free* archive areas.

The Debian archive maintainers provide the authoritative list of
sections. At present, they are: admin, cli-mono, comm, database,
debug, devel, doc, editors, education, electronics, embedded, fonts,
games, gnome, gnu-r, gnustep, graphics, hamradio, haskell, httpd,
interpreters, introspection, java, javascript, kde, kernel, libdevel,
libs, lisp, localization, mail, math, metapackages, misc, net, news,
ocaml, oldlibs, otherosfs, perl, php, python, ruby, rust, science,
shells, sound, tasks, tex, text, utils, vcs, video, web, x11, xfce,
zope. The additional section *debian-installer* contains special
packages used by the installer and is not used for normal Debian
packages.

For more information about the sections and their definitions, see the
list of sections in unstable.


2.5. Priorities
===============

Each package must have a *priority* value, which is set in the
metadata for the Debian archive and is also included in the package's
binary control (see Priority), ".dsc" and ".changes" files. This
information is used to control which packages are included in standard
or minimal Debian installations.

Starting with dpkg version 1.22.13, the *Priority* of a binary package
is set to "optional" unless specified otherwise in the source or its
binary stanza in the source package template control file. Therefore,
explicitly specifying *Priority* as "optional" may be omitted.

Most Debian packages will have a priority of "optional". Priority
levels other than "optional" are only used for packages that should be
included by default in a standard installation of Debian.

The priority of a package is determined solely by the functionality it
provides directly to the user. The priority of a package should not be
increased merely because another higher-priority package depends on
it; instead, the tools used to construct Debian installations will
correctly handle package dependencies. In particular, this means that
C-like libraries will almost never have a priority above "optional",
since they do not provide functionality directly to users. However, as
an exception, the maintainers of Debian installers may request an
increase of the priority of a package to resolve installation issues
and ensure that the correct set of packages is included in a standard
or minimal install.

The following *priority levels* are recognized by the Debian package
management tools.

"required"
   Packages which are necessary for the proper functioning of the
   system (usually, this means that dpkg functionality depends on
   these packages). Removing a "required" package may cause your
   system to become totally broken and you may not even be able to use
   "dpkg" to put things back, so only do so if you know what you are
   doing.

   Systems with only the "required" packages installed have at least
   enough functionality for the sysadmin to boot the system and
   install more software.

"important"
   Important programs, including those which one would expect to find
   on any Unix-like system. If the expectation is that an experienced
   Unix person who found it missing would say "What on earth is going
   on, where is "foo"?", it must be an "important" package.  [6] Other
   packages without which the system will not run well or be usable
   must also have priority "important". This does *not* include Emacs,
   the X Window System, TeX or any other large applications. The
   "important" packages are just a bare minimum of commonly-expected
   and necessary tools.

"standard"
   These packages provide a reasonably small but not too limited
   character-mode system. This is what will be installed by default if
   the user doesn't select anything else. It doesn't include many
   large applications.

   Two packages that both have a priority of "standard" or higher must
   not conflict with each other.

"optional"
   This is the default priority for the majority of the archive.
   Unless a package should be installed by default on standard Debian
   systems, it should have a priority of "optional". Packages with a
   priority of "optional" may conflict with each other.

"extra"
   *This priority is deprecated.* Use the "optional" priority instead.
   This priority should be treated as equivalent to "optional".

   The "extra" priority was previously used for packages that
   conflicted with other packages and packages that were only likely
   to be useful to people with specialized requirements. However, this
   distinction was somewhat arbitrary, not consistently followed, and
   not useful enough to warrant the maintenance effort.

[6] This is an important criterion because we are trying to produce,
    amongst other things, a free Unix.



3. Binary packages
******************

The Debian distribution is based on the Debian package management
system, called "dpkg". Thus, all packages in the Debian distribution
must be provided in the ".deb" file format.

A ".deb" package contains two sets of files: a set of files to install
on the system when the package is installed, and a set of files that
provide additional metadata about the package or which are executed
when the package is installed or removed. This second set of files is
called *package metadata files*. Among those files are the package
maintainer scripts and "control", the binary package control file that
contains the control fields for the package. Other package metadata
files include symbols or shlibs used to store shared library
dependency information and the "conffiles" file that lists the
package's configuration files (described in Configuration files).

There is unfortunately a collision of terminology here between control
information files and files in the Debian control file format.
Throughout this document, a *control file* refers to a file in the
Debian control file format. These files are documented in Control
files and their fields. Only files referred to specifically as
*package metadata files* are the files included in the package
metadata member (called "control.tar") of the ".deb" file format used
by binary packages. Most package metadata files are not in the Debian
control file format.


3.1. The package name
=====================

Every package must have a name that's unique within the Debian
archive.

The package name is included in the control field "Package", the
format of which is described in Package. The package name is also
included as a part of the file name of the ".deb" file.


3.1.1. Packages with potentially offensive content
--------------------------------------------------

As a maintainer you should make a judgement about whether the contents
of a package is appropriate to include, whether it needs any kind of
content warning, and whether some parts should be split out into a
separate package (so that users who want to avoid certain parts can do
so).  In making these decisions you should take into account the
project's views as expressed in our Diversity Statement.

If you split out (potentially) offensive or disturbing material into a
separate package, you should usually mark this in the package name by
adding "-offensive".  For example, "cowsay" vs "cowsay-offensive".  In
this situation the "-offensive" package can be Suggested by the core
package(s), but should not be Recommended or Depended on.


3.2. The version of a package
=============================

Every package has a version number recorded in its "Version" control
file field, described in Version.

The package management system imposes an ordering on version numbers,
so that it can tell whether packages are being up- or downgraded and
so that package system front end applications can tell whether a
package it finds available is newer than the one installed on the
system. The version number format has the most significant parts (as
far as comparison is concerned) at the beginning.

If an upstream package has problematic version numbers they should be
converted to a sane form for use in the "Version" field.


3.2.1. Version numbers based on dates
-------------------------------------

In general, Debian packages should use the same version numbers as the
upstream sources. However, upstream version numbers based on some date
formats (sometimes used for development or "snapshot" releases) will
not be ordered correctly by the package management software. For
example, "dpkg" will consider "96May01" to be greater than "96Dec24".

To prevent having to use epochs for every new upstream version, the
date-based portion of any upstream version number should be given in a
way that sorts correctly: four-digit year first, followed by a two-
digit numeric month, followed by a two-digit numeric day-of-month,
possibly with punctuation between the components.

Native Debian packages (i.e., packages which have been written
especially for Debian) whose version numbers include dates should also
follow these rules. If punctuation is desired between the date
components, remember that hyphen ("-") cannot be used in native
version numbers. Period (".") is normally a good choice.


3.2.2. Uniqueness of version numbers
------------------------------------

The part of the version number after the epoch must not be reused for
a version of the package with different contents once the package has
been accepted into the archive, even if the version of the package
previously using that part of the version number is no longer present
in any archive suites.

This uniqueness requirement applies to the version numbers of source
packages and of binary packages, even if the source package producing
a given binary package changes.  Thus the version numbers which a
binary package must not reuse includes the version numbers of any
versions of the binary package ever accepted into the archive, under
any source package.

Additionally, for non-native packages, the upstream version must not
be reused for different upstream source code, so that for each source
package name and upstream version number there exists exactly one
original source archive contents (see Files).

The reason for these restrictions is as follows.  Epochs are not
included in the names of the files that compose source packages, or in
the filenames of binary packages, so reusing a version number, even if
the epoch differs, results in identically named files with different
contents.  This can cause various problems.

If you find yourself wanting to reuse the part of a version number
after the epoch, you can just increment the Debian revision, which
doesn't need to start at 1 or be consecutive.


3.3. The maintainer of a package
================================

Every package must have a maintainer, except for orphaned packages as
described below. The maintainer may be one person or a group of people
reachable from a common email address, such as a mailing list. The
maintainer is responsible for maintaining the Debian packaging files,
evaluating and responding appropriately to reported bugs, uploading
new versions of the package (either directly or through a sponsor),
ensuring that the package is placed in the appropriate archive area
and included in Debian releases as appropriate for the stability and
utility of the package, and requesting removal of the package from the
Debian distribution if it is no longer useful or maintainable.

The maintainer must be specified in the "Maintainer" control field
with their correct name and a working email address. The email address
given in the "Maintainer" control field must accept mail from those
role accounts in Debian used to send automated mails regarding the
package. This includes non-spam mail from the bug-tracking system, all
mail from the Debian archive maintenance software, and other role
accounts or automated processes that are commonly agreed on by the
project.  [1] If one person or team maintains several packages, they
should use the same form of their name and email address in the
"Maintainer" fields of those packages.

The format of the "Maintainer" control field is described in
Maintainer.

If the maintainer of the package is a team of people with a shared
email address, the "Uploaders" control field must be present and must
contain at least one human with their personal email address. See
Uploaders for the syntax of that field.

An orphaned package is one with no current maintainer. Orphaned
packages should have their "Maintainer" control field set to "Debian
QA Group <packages@qa.debian.org>". These packages are considered
maintained by the Debian project as a whole until someone else
volunteers to take over maintenance.  [2]


3.4. The description of a package
=================================

Every Debian package must have a "Description" control field which
contains a synopsis and extended description of the package. Technical
information about the format of the "Description" field is in
Description.

The description should describe the package (the program) to a user
(system administrator) who has never met it before so that they have
enough information to decide whether they want to install it. This
description should not just be copied verbatim from the program's
documentation.

Put important information first, both in the synopsis and extended
description. Sometimes only the first part of the synopsis or of the
description will be displayed. You can assume that there will usually
be a way to see the whole extended description.

The description should also give information about the significant
dependencies and conflicts between this package and others, so that
the user knows why these dependencies and conflicts have been
declared.

Instructions for configuring or using the package should not be
included (that is what installation scripts, manual pages, info files,
etc., are for). Copyright statements and other administrivia should
not be included either (that is what the copyright file is for).


3.4.1. The single line synopsis
-------------------------------

The single line synopsis should be kept brief---certainly under 80
characters.

Do not include the package name in the synopsis line. The display
software knows how to display this already, and you do not need to
state it. Remember that in many situations the user may only see the
synopsis line - make it as informative as you can.


3.4.2. The extended description
-------------------------------

Do not try to continue the single line synopsis into the extended
description. This will not work correctly when the full description is
displayed, and makes no sense where only the summary (the single line
synopsis) is available.

The extended description should describe what the package does and how
it relates to the rest of the system (in terms of, for example, which
subsystem it is which part of).

The description field needs to make sense to anyone, even people who
have no idea about any of the things the package deals with.  [3]


3.5. Dependencies
=================

Every package must specify the dependency information about other
packages that are required for the first to work correctly.

For example, a dependency entry must be provided for any shared
libraries required by a dynamically-linked executable binary in a
package.

Packages are not required to declare any dependencies they have on
other packages which are marked "Essential" (see below), and should
not do so unless they depend on a particular version of that package.
[4]

Sometimes, unpacking one package requires that another package be
first unpacked *and* configured. In this case, the depending package
must specify this dependency in the "Pre-Depends" control field.

You should not specify a "Pre-Depends" entry for a package before this
has been discussed on the "debian-devel" mailing list and a consensus
about doing that has been reached.

The format of the package interrelationship control fields is
described in Declaring relationships between packages.


3.6. Virtual packages
=====================

Sometimes, there are several packages which offer more-or-less the
same functionality. In this case, it's useful to define a *virtual
package* whose name describes that common functionality. (The virtual
packages only exist logically, not physically; that's why they are
called *virtual*.) The packages with this particular function will
then *provide* the virtual package. Thus, any other package requiring
that function can simply depend on the virtual package without having
to specify all possible packages individually.

All packages should use virtual package names where appropriate, and
arrange to create new ones if necessary. They should not use virtual
package names (except privately, amongst a cooperating group of
packages) unless they have been agreed upon and appear in the list of
virtual package names. (See also Virtual packages - Provides)

The latest version of the authoritative list of virtual package names
can be found in the "debian-policy" package. It is also available from
the Debian web mirrors at https://www.debian.org/doc/packaging-manuals
/virtual-package-names-list.yaml.

The procedure for updating the list is described in the preface to the
list.


3.7. Base system
================

The "base system" is a minimum subset of the Debian system that is
installed before everything else on a new system. Only very few
packages are allowed to form part of the base system, in order to keep
the required disk usage very small.

The base system consists of all those packages with priority
"required" or "important". Many of them will be tagged "essential"
(see below).


3.8. Essential packages
=======================

Essential is defined as the minimal set of functionality that must be
available and usable on the system at all times, even when packages
are in the "Unpacked" state. Packages are tagged "essential" for a
system using the "Essential" control field. The format of the
"Essential" control field is described in Essential.

Since these packages cannot be easily removed (one has to specify an
extra *force option* to "dpkg" to do so), this flag must not be used
unless absolutely necessary. A shared library package must not be
tagged "essential"; dependencies will prevent its premature removal,
and we need to be able to remove it when it has been superseded.

Since dpkg will not prevent upgrading of other packages while an
"essential" package is in an unconfigured state, all "essential"
packages must supply all of their core functionality even when
unconfigured after being configured at least once. If the package
cannot satisfy this requirement it must not be tagged as essential,
and any packages depending on this package must instead have explicit
dependency fields as appropriate.

Maintainers should take great care in adding any programs, interfaces,
or functionality to "essential" packages. Packages may assume that
functionality provided by "essential" packages is always available
without declaring explicit dependencies, which means that removing
functionality from the Essential set is very difficult and is almost
never done. Any capability added to an "essential" package therefore
creates an obligation to support that capability as part of the
Essential set in perpetuity.

You must not tag any packages "essential" before this has been
discussed on the "debian-devel" mailing list and a consensus about
doing that has been reached.


3.9. Maintainer Scripts
=======================

The package installation scripts should avoid producing output which
is unnecessary for the user to see and should rely on "dpkg" to stave
off boredom on the part of a user installing many packages. This
means, amongst other things, not passing the "--verbose" option to
"update-alternatives".

Errors which occur during the execution of an installation script must
be checked and the installation must not continue after an error.

Note that in general Scripts applies to package maintainer scripts,
too.

You should not use "dpkg-divert" on a file belonging to another
package without consulting the maintainer of that package first. When
adding or removing diversions, package maintainer scripts must provide
the "--package" flag to "dpkg-divert" and must not use "--local".

All packages which supply an instance of a common command name (or, in
general, filename) should generally use "update-alternatives" so that
they can be installed together. If "update-alternatives" is not used,
then each package must use "Conflicts" to ensure that other packages
are removed. (In this case, it may be appropriate to specify a
conflict against earlier versions of something that previously did not
use "update-alternatives"; this is an exception to the usual rule that
versioned conflicts should be avoided.)

Diversions are primarily intended as a tool for local administrators
and local packages to override the behavior of Debian.  While there
are some circumstances where one Debian package may need to divert a
file installed by another Debian package, such circumstances are rare.
Maintainers should strongly prefer using other overriding mechanisms,
instead of diversions, whenever those other mechanisms are sufficient
to accomplish the same goal. In other words, diversions in packages
should be considered a last resort. Diversion of a file in one Debian
package by another Debian package should be coordinated between the
maintainers of those packages.

One specific case of this rule is that configuration files used by
"systemd" components, such as units, udev rules, tmpfiles.d, modules-
load.d, sysusers and other such files, including those specific to
systemd daemons (e.g.:  /etc/systemd/system.conf). must not be
diverted by any Debian package. Instead, use masking and drop-ins.

Alternatives must not be used for "systemd" configuration files. The
alternatives system does not know how to apply changes to services
when updating alternatives, so the resulting behavior would be
confusing and unpredictable. Instead, aliases can be used to provide
alternative implementations of the same named unit.


3.9.1. Prompting in maintainer scripts
--------------------------------------

Package maintainer scripts may prompt the user if necessary. Prompting
must be done by communicating through a program, such as "debconf",
which conforms to the Debian Configuration Management Specification,
version 2 or higher.

Packages which are essential, or which are dependencies of essential
packages, may fall back on another prompting method if no such
interface is available when they are executed.

The Debian Configuration Management Specification is included in the
"debconf_specification" files in the debian-policy package. It is also
available from the Debian web mirrors at https://www.debian.org/doc
/packaging-manuals/debconf_specification.html.

Packages which use the Debian Configuration Management Specification
may contain the additional package metadata files "config" and
"templates". "config" is an additional maintainer script used for
package configuration, and "templates" contains templates used for
user prompting. The "config" script might be run before the "preinst"
script and before the package is unpacked or any of its dependencies
or pre-dependencies are satisfied. Therefore it must work using only
the tools present in *essential* packages.  [5]

Packages which use the Debian Configuration Management Specification
must allow for translation of their user-visible messages by using a
gettext-based system such as the one provided by the po-debconf
package.

Packages should try to minimize the amount of prompting they need to
do, and they should ensure that the user will only ever be asked each
question once. This means that packages should try to use appropriate
shared configuration files (such as "/etc/papersize" and
"/etc/news/server"), and shared debconf variables rather than each
prompting for their own list of required pieces of information.

It also means that an upgrade should not ask the same questions again,
unless the user has used "dpkg --purge" to remove the package's
configuration. The answers to configuration questions should be stored
in an appropriate place in "/etc" so that the user can modify them,
and how this has been done should be documented.

If a package has a vitally important piece of information to pass to
the user (such as "don't run me as I am, you must edit the following
configuration files first or you risk your system emitting badly-
formatted messages"), it should display this in the "config" or
"postinst" script and prompt the user to hit return to acknowledge the
message. Copyright messages do not count as vitally important (they
belong in "/usr/share/doc/PACKAGE/copyright"); neither do instructions
on how to use a program (these should be in on-line documentation,
where all the users can see them).

Any necessary prompting should almost always be confined to the
"config" or "postinst" script. If it is done in the "postinst", it
should be protected with a conditional so that unnecessary prompting
doesn't happen if a package's installation fails and the "postinst" is
called with "abort-upgrade", "abort-remove" or "abort-deconfigure".

[1] A sample implementation of such a whitelist written for the
    Mailman mailing list management software is used for mailing lists
    hosted by https://alioth-lists.debian.net/.

[2] The detailed procedure for gracefully orphaning a package can be
    found in the Debian Developer's Reference (see Related documents).

[3] The blurb that comes with a program in its announcements and/or
    "README" files is rarely suitable for use in a description. It is
    usually aimed at people who are already in the community where the
    package is used.

[4] Essential is needed in part to avoid unresolvable dependency loops
    on upgrade. If packages add unnecessary dependencies on packages
    in this set, the chances that there **will** be an unresolvable
    dependency loop caused by forcing these Essential packages to be
    configured first before they need to be is greatly increased. It
    also increases the chances that frontends will be unable to
    **calculate** an upgrade path, even if one exists.

    Also, functionality is rarely ever removed from the Essential set,
    but *packages* have been removed from the Essential set when the
    functionality moved to a different package. So depending on these
    packages *just in case* they stop being essential does way more
    harm than good.

[5] Debconf or another tool that implements the Debian Configuration
    Management Specification will also be installed, and any versioned
    dependencies on it will be satisfied before preconfiguration
    begins.



4. Source packages
******************

A Debian source package contains the source material used to construct
one or more binary packages.  A source package consists of a ".dsc"
file (see Debian source package control files -- .dsc), one or more
compressed tar files, and possibly other files depending on the type
and format of source package.  Binary packages are contructed from the
source package via a build process defined by "debian/rules" and other
files in the "debian" directory of the unpacked source package.

Debian source packages are classified as *native* or *non-native*.

A native source package is one that does not distinguish between
Debian packaging releases and upstream releases.  A native source
package contains a single tar file of source material, and the
versioning does not have a Debian-specific component.  Native packages
are normally (but not exclusively) used for software that has no
independent existence outside of Debian, such as software written
specifically to be a Debian package.

A non-native source package separates the upstream release from the
Debian packaging and any Debian-specific changes.  The source in a
non-native source package is divided into one or more upstream tar
files plus a collection of Debian-specific files.  (Depending on the
format of the source package, those Debian-specific files may come in
the form of another tar file or in the form of a compressed diff.)
The version of a non-native package has an upstream component and a
Debian component, and there may be multiple Debian package versions
associated with a single upstream release version and sharing the same
upstream source tar files.

Most source packages in Debian are non-native.


4.1. Standards conformance
==========================

Source packages should specify the most recent version number of this
policy document with which your package complied when it was last
updated.

The version is specified in the "Standards-Version" control field. The
format of the "Standards-Version" field is described in Standards-
Version.

For a package to have an old Standards-Version value is not *itself* a
bug, however.  It just means that no-one has yet reviewed the package
with changes to the standards in mind.

When updating existing packaging, the Standards-Version must not be
updated except after reviewing the changes between the old and the new
versions of the standards and updating your package if necessary (the
Upgrading checklist can help with this task).

A very old Standards-Version can mean that infelicities in the package
are likely.  It is recommended that each package be reviewed at least
once per Debian release, so a Standards-Version older than the
previous Debian release is indicative of work (if only review work)
that needs doing.


4.2. Package relationships
==========================

Source packages should specify which binary packages they require to
be installed or not to be installed in order to build correctly. For
example, if building a package requires a certain compiler, then the
compiler should be specified as a build-time dependency.

It is not necessary to explicitly specify build-time relationships on
a minimal set of packages that are always needed to compile, link and
put in a Debian package a standard "Hello World!" program written in C
or C++. The required packages are called *build-essential*, and an
informational list can be found in "/usr/share/doc/build-
essential/list" (which is contained in the "build-essential" package).
[1]

When specifying the set of build-time dependencies, one should list
only those packages explicitly required by the build. It is not
necessary to list packages which are required merely because some
other package in the list of build-time dependencies depends on them.
[2]

If build-time dependencies are specified, it must be possible to build
the package and produce working binaries on a system with only
essential and build-essential packages installed and also those
required to satisfy the build-time relationships (including any
implied relationships). In particular, this means that version clauses
should be used rigorously in build-time relationships so that one
cannot produce bad or inconsistently configured packages when the
relationships are properly satisfied.

Declaring relationships between packages explains the technical
details.


4.3. Changes to the upstream sources
====================================

If changes to the source code are made that are not specific to the
needs of the Debian system, they should be sent to the upstream
authors in whatever form they prefer so as to be included in the
upstream version of the package.

If you need to configure the package differently for Debian or for
Linux, and the upstream source doesn't provide a way to do so, you
should add such configuration facilities (for example, a new
"autoconf" test or "#define") and send the patch to the upstream
authors, with the default set to the way they originally had it. You
can then easily override the default in your "debian/rules" or
wherever is appropriate.

You should make sure that the "configure" utility detects the correct
architecture specification string (refer to Architecture specification
strings for details).

If your package includes the scripts "config.sub" and "config.guess",
you should arrange for the versions provided by the package autotools-
dev be used instead (see autotools-dev documentation for details how
to achieve that). This ensures that these files can be updated
distribution-wide at build time when introducing new architectures.

If you need to edit a "Makefile" where GNU-style "configure" scripts
are used, you should edit the ".in" files rather than editing the
"Makefile" directly. This allows the user to reconfigure the package
if necessary. You should *not* configure the package and edit the
generated "Makefile"! This makes it impossible for someone else to
later reconfigure the package without losing the changes you made.


4.4. Debian changelog: "debian/changelog"
=========================================

Every source package must include the Debian changelog file,
"debian/changelog".  Changes in the Debian version of the package
should be briefly explained in this file.  [3] This includes
modifications made in the Debian package compared to the upstream one
as well as other changes and updates to the package.  [4]

The format of the "debian/changelog" allows the package building tools
to discover which version of the package is being built and find out
other release-specific information.

That format is a series of entries like this:

   package (version) distribution(s); urgency=urgency
     [optional blank line(s), stripped]
     * change details
     more change details
     [blank line(s), included in output of dpkg-parsechangelog]
     * even more change details
     [optional blank line(s), stripped]
    -- maintainer name <email address>[two spaces]  date

"package" and "version" are the source package name and version
number.

"distribution(s)" lists the distributions where this version should be
installed when it is uploaded - it is copied to the "Distribution"
field in the ".changes" file. See Distribution.

"urgency" is the value for the "Urgency" field in the ".changes" file
for the upload (see Urgency). It is not possible to specify an urgency
containing commas; commas are used to separate "keyword=value"
settings in the "dpkg" changelog format (though there is currently
only one useful keyword, "urgency").

The change details may in fact be any series of lines starting with at
least two spaces, but conventionally each change starts with an
asterisk and a separating space and continuation lines are indented so
as to bring them in line with the start of the text above. Blank lines
may be used here to separate groups of changes, if desired.

If this upload resolves bugs recorded in the Bug Tracking System
(BTS), they may be automatically closed on the inclusion of this
package into the Debian archive by including the string: "closes:
Bug#nnnnn" in the change details, where "#nnnnn" is the bug number.
[5] This information is conveyed via the "Closes" field in the
".changes" file (see Closes).

The maintainer name and email address used in the changelog should be
the details of the person who prepared this release of the package.
They are *not* necessarily those of the uploader or usual package
maintainer. [6] The information here will be copied to the "Changed-
By" field in the ".changes" file (see Changed-By), and then later used
to send an acknowledgement when the upload has been installed.

The date has the following format  [7] (compatible and with the same
semantics of RFC 2822 and RFC 5322):

   day-of-week, dd month yyyy hh:mm:ss +zzzz

where:

* "day-of-week" is one of: Mon, Tue, Wed, Thu, Fri, Sat, Sun

* "dd" is a one- or two-digit day of the month (01-31)

* "month" is one of: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct,
  Nov, Dec

* "yyyy" is the four-digit year (e.g. 2010)

* "hh" is the two-digit hour (00-23)

* "mm" is the two-digit minutes (00-59)

* "ss" is the two-digit seconds (00-60)

* "+zzzz" or "-zzzz" is the time zone offset from Coordinated
     Universal Time (UTC). "+" indicates that the time is ahead of
     (i.e., east of) UTC and "-" indicates that the time is behind
     (i.e., west of) UTC.  The first two digits indicate the hour
     difference from UTC and the last two digits indicate the number
     of additional minutes difference from UTC. The last two digits
     must be in the range 00-59.

The first "title" line with the package name must start at the left
hand margin. The "trailer" line with the maintainer and date details
must be preceded by exactly one space. The maintainer details and the
date must be separated by exactly two spaces.

The entire changelog must be encoded in UTF-8.

For more information on placement of the changelog files within binary
packages, please see Changelog files and release notes.


4.5. Copyright: "debian/copyright"
==================================

Every package must be accompanied by a verbatim copy of its
distribution license(s) in the file
"/usr/share/doc/PACKAGE/copyright".

This file is often required to contain a verbatim copy of the
package's copyright information, too; see Copyright information and
Copyright considerations for details, and for further considerations
related to copyrights for packages.


4.6. Error trapping in makefiles
================================

When "make" invokes a command in a makefile (including your package's
upstream makefiles and "debian/rules"), it does so using "sh". This
means that "sh"'s usual bad error handling properties apply: if you
include a miniature script as one of the commands in your makefile
you'll find that if you don't do anything about it then errors are not
detected and "make" will blithely continue after problems.

Every time you put more than one shell command (this includes using a
loop) in a makefile command you must make sure that errors are
trapped. For simple compound commands, such as changing directory and
then running a program, using "&&" rather than semicolon as a command
separator is sufficient. For more complex commands including most
loops and conditionals you should include a separate "set -e" command
at the start of every makefile command that's actually one of these
miniature shell scripts.


4.7. Time Stamps
================

Maintainers should preserve the modification times of the upstream
source files in a package, as far as is reasonably possible.  [8]


4.8. Restrictions on objects in source packages
===============================================

The source package must not contain device special files, sockets, or
setuid or setgid files. [9]


4.9. Main building script: "debian/rules"
=========================================

This file must be an executable makefile.  It contains the package-
specific recipes for compiling the source (if required) and
constructing one or more binary packages.

"debian/rules" must start with the line "#!/usr/bin/make -f", so that
it can be invoked by saying its name rather than invoking "make"
explicitly.  That is, invoking either of "make -f debian/rules
args..." or "./debian/rules args..." must result in identical
behavior.

The recommended way to implement the build process of a Debian
package, in the absence of a good reason to use a different approach,
is the "dh" tool.  This includes the contents of the "debian/rules"
building script. "dh" is the most common packaging helper tool in
Debian.  Using it will usually save effort in complying with the rules
in this document, because "dh" will automatically implement many of
them without requiring explicit instructions.

There are sometimes good reasons to use a different approach.  For
example, the standard tools for packaging software written in some
languages may use another tool; some rarer packaging patterns, such as
multiple builds of the same software with different options, are
easier to express with other tools; and a packager working on a
different packaging helper might want to use their tool.  The
recommendation to use "dh" does not always apply, and use of "dh" is
not required.

For more information about how to use "dh", see the documentation in
the debhelper package, most notably the *dh(1)* manual page.

The following targets are required and must be implemented by
"debian/rules": "clean", "binary", "binary-arch", "binary-indep",
"build", "build-arch" and "build-indep". These are the targets called
by "dpkg-buildpackage".

Since an interactive "debian/rules" script makes it impossible to
auto-compile that package and also makes it hard for other people to
reproduce the same binary package, all required targets must be non-
interactive. It also follows that any target that these targets depend
on must also be non-interactive.

The package build should be as verbose as reasonably possible, except
where the "terse" tag is included in "DEB_BUILD_OPTIONS" (see
debian/rules and DEB_BUILD_OPTIONS).  This makes life easier for
porters and bug squashers more generally, who can look at build logs
for possible problems.  To accomplish this, "debian/rules" should pass
to the commands it invokes options that cause them to produce verbose
output. For example, the build target should pass "--disable-silent-
rules" to any configure scripts.  See also Binaries.

Except for packages in the non-free archive with the "Autobuild"
control field unset or set to "no", required targets must not attempt
network access to other hosts.  Only access via the loopback interface
to services on the build host that have been started by the build is
allowed.

Required targets must not attempt to write outside of the unpacked
source package tree.  There are two exceptions.  Firstly, the binary
targets may write the binary packages to the parent directory of the
unpacked source package tree.  Secondly, required targets may write to
"/tmp", "/var/tmp" and to the directory specified by the "TMPDIR"
environment variable, but must not depend on the contents of any of
these.

This restriction is intended to prevent source package builds creating
and depending on state outside of themselves, thus affecting multiple
independent rebuilds.  In particular, the required targets must not
attempt to write into "HOME".

The targets are as follows:

"build" (required)
   The "build" target should perform all the configuration and
   compilation of the package. If a package has an interactive pre-
   build configuration routine, the Debian source package must either
   be built after this has taken place (so that the binary package can
   be built without rerunning the configuration) or the configuration
   routine modified to become non-interactive. (The latter is
   preferable if there are architecture-specific features detected by
   the configuration routine.)

   For some packages, notably ones where the same source tree is
   compiled in different ways to produce two binary packages, the
   "build" target does not make much sense. For these packages it is
   good enough to provide two (or more) targets ("build-a" and
   "build-b" or whatever) for each of the ways of building the
   package, and a "build" target that does nothing. The "binary"
   target will have to build the package in each of the possible ways
   and make the binary package out of each.

   The "build" target must not do anything that might require root
   privilege.

   The "build" target may need to run the "clean" target first - see
   below.

   When a package has a configuration and build routine which takes a
   long time, or when the makefiles are poorly designed, or when
   "build" needs to run "clean" first, it is a good idea to "touch
   build" when the build process is complete. This will ensure that if
   "debian/rules build" is run again it will not rebuild the whole
   program. [10]

"build-arch" (required), "build-indep" (required)
   The "build-arch" target must perform all the configuration and
   compilation required for producing all architecture-dependent
   binary packages (those packages for which the body of the
   "Architecture" field in "debian/control" is not "all"). Similarly,
   the "build-indep" target must perform all the configuration and
   compilation required for producing all architecture-independent
   binary packages (those packages for which the body of the
   "Architecture" field in "debian/control" is "all"). The "build"
   target should either depend on those targets or take the same
   actions as invoking those targets would perform.  [11]

   The "build-arch" and "build-indep" targets must not do anything
   that might require root privilege.

"binary" (required), "binary-arch" (required), "binary-indep"
(required)
   The "binary" target must be all that is necessary for the user to
   build the binary package(s) produced from this source package. It
   is split into two parts: "binary-arch" builds the binary packages
   which are specific to a particular architecture, and "binary-indep"
   builds those which are not.

   "binary" may be (and commonly is) a target with no commands which
   simply depends on "binary-arch" and "binary-indep".

   Both "binary-*" targets should depend on the "build" target, or on
   the appropriate "build-arch" or "build-indep" target, so that the
   package is built if it has not been already. It should then create
   the relevant binary package(s), using "dpkg-gencontrol" to make
   their control files and "dpkg-deb" to build them and place them in
   the parent of the top level directory.

   Both the "binary-arch" and "binary-indep" targets *must* exist. If
   one of them has nothing to do (which will always be the case if the
   source generates only a single binary package, whether
   architecture-dependent or not), it must still exist and must always
   succeed.

   The "binary" targets may need to be invoked as root depending on
   the value of the Rules-Requires-Root field.  [12]

"clean" (required)
   This must undo any effects that the "build" and "binary" targets
   may have had, except that it should leave alone any output files
   created in the parent directory by a run of a "binary" target.

   If a "build" file is touched at the end of the "build" target, as
   suggested above, it should be removed as the first action that
   "clean" performs, so that running "build" again after an
   interrupted "clean" doesn't think that everything is already done.

   The "clean" target may need to be invoked as root if "binary" has
   been invoked since the last "clean", or if "build" has been invoked
   as root (since "build" may create directories, for example).

   The "clean" target cannot be used to remove files in the source
   tree that are not compatible with the DFSG. This is because the
   files would remain in the upstream tarball, and thus in the source
   package, so the source package would continue to violate DFSG.
   Instead, the upstream source should be repacked to remove those
   files.

"patch" (optional)
   This target performs whatever additional actions are required to
   make the source ready for editing (unpacking additional upstream
   archives, applying patches, etc.). It is recommended to be
   implemented for any package where "dpkg-source -x" does not result
   in source ready for additional modification. See Source package
   handling: debian/README.source.

The "build", "binary" and "clean" targets must be invoked with the
current directory being the package's top-level directory.

Additional targets may exist in "debian/rules", either as published or
undocumented interfaces or for the package's internal use.

The architectures we build on and build for are determined by "make"
variables using the utility "dpkg-architecture". You can determine the
Debian architecture and the GNU style architecture specification
string for the build architecture as well as for the host
architecture. The build architecture is the architecture on which
"debian/rules" is run and the package build is performed. The host
architecture is the architecture on which the resulting package will
be installed and run. The target architecture is the architecture of
the packages that the compiler currently being built will generate.
These are normally the same, but may be different in the case of
cross-compilation (building packages for one architecture on machines
of a different architecture), building a cross-compiler (a compiler
package that will generate objects for one architecture, built on a
machine of a different architecture) or a Canadian cross-compiler (a
compiler that will generate objects for one architecture, built on a
machine of a different architecture, that will run on yet a different
architecture).

Here is a list of supported "make" variables:

* "DEB_*_ARCH" (the Debian architecture)

* "DEB_*_ARCH_CPU" (the Debian CPU name)

* "DEB_*_ARCH_BITS" (the Debian CPU pointer size in bits)

* "DEB_*_ARCH_ENDIAN" (the Debian CPU endianness)

* "DEB_*_ARCH_OS" (the Debian System name)

* "DEB_*_GNU_TYPE" (the GNU style architecture specification string)

* "DEB_*_GNU_CPU" (the CPU part of "DEB_*_GNU_TYPE")

* "DEB_*_GNU_SYSTEM" (the System part of "DEB_*_GNU_TYPE")

where "*" is either "BUILD" for specification of the build
architecture, "HOST" for specification of the host architecture or
"TARGET" for specification of the target architecture.

Backward compatibility can be provided in the rules file by setting
the needed variables to suitable default values; please refer to the
documentation of "dpkg-architecture" for details.

It is important to understand that the "DEB_*_ARCH" string only
determines which Debian architecture we are building on or for. It
should not be used to get the CPU or system information; the
"DEB_*_ARCH_CPU" and "DEB_*_ARCH_OS" variables should be used for
that. GNU style variables should generally only be used with upstream
build systems.

The builder may set "DEB_RULES_REQUIRES_ROOT" environment variable
when calling any of the mandatory targets as defined in Rules-
Requires-Root.  If the variable is not set, the package must behave as
if it was set to "binary-targets".


4.9.1. "debian/rules" and "DEB_BUILD_OPTIONS"
---------------------------------------------

Supporting the standardized environment variable "DEB_BUILD_OPTIONS"
is recommended. This variable can contain several flags to change how
a package is compiled and built. Each flag must be in the form flag or
flag=options. If multiple flags are given, they must be separated by
whitespace.  [13] flag must start with a lowercase letter ("a-z") and
consist only of lowercase letters, numbers ("0-9"), and the characters
"-" and "_" (hyphen and underscore). options must not contain
whitespace. The same tag should not be given multiple times with
conflicting values. Package maintainers may assume that
"DEB_BUILD_OPTIONS" will not contain conflicting tags.

The meaning of the following tags has been standardized:

"nocheck"
   This tag says to not run any build-time test suite provided by the
   package.

"nodoc"
   This tag says to skip any build steps that only generate package
   documentation. Files required by other sections of Debian Policy,
   such as copyright and changelog files, must still be generated and
   put in the package, but other generated documentation such as
   help2man-generated pages, Doxygen-generated API documentation, or
   info pages generated from Texinfo sources should be skipped if
   possible. This option does not change the set of binary packages
   generated by the source package, but documentation-only binary
   packages may be nearly empty when built with this option.

"noopt"
   The presence of this tag means that the package should be compiled
   with a minimum of optimization. For C programs, it is best to add
   "-O0" to "CFLAGS" (although this is usually the default). Some
   programs might fail to build or run at this level of optimization;
   it may be necessary to use "-O1", for example.

"nostrip"
   This tag means that the debugging symbols should not be stripped
   from the binary during installation, so that debugging information
   may be included in the package.

"parallel=n"
   This tag means that the package should be built using up to "n"
   parallel processes if the package build system supports this.  [14]
   If the package build system does not support parallel builds, this
   string must be ignored. If the package build system only supports a
   lower level of concurrency than n, the package should be built
   using as many parallel processes as the package build system
   supports. It is up to the package maintainer to decide whether the
   package build times are long enough and the package build system is
   robust enough to make supporting parallel builds worthwhile.

"terse"
   This tag means that the package build will be less verbose than
   default.  For example, "debian/rules" might pass options to the
   package's configure script that cause the compiler to produce less
   output.

Unknown flags must be ignored by "debian/rules".

The following makefile snippet is an example of how one may implement
the build options; you will probably have to massage this example in
order to make it work for your package.

   CFLAGS = -Wall -g
   INSTALL = install
   INSTALL_FILE    = $(INSTALL) -p    -o root -g root  -m  644
   INSTALL_PROGRAM = $(INSTALL) -p    -o root -g root  -m  755
   INSTALL_SCRIPT  = $(INSTALL) -p    -o root -g root  -m  755
   INSTALL_DIR     = $(INSTALL) -p -d -o root -g root  -m  755

   ifneq (,$(filter noopt,$(DEB_BUILD_OPTIONS)))
       CFLAGS += -O0
   else
       CFLAGS += -O2
   endif
   ifeq (,$(filter nostrip,$(DEB_BUILD_OPTIONS)))
       INSTALL_PROGRAM += -s
   endif
   ifneq (,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))
       NUMJOBS = $(patsubst parallel=%,%,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))
       MAKEFLAGS += -j$(NUMJOBS)
   endif

   build:
           # ...
   ifeq (,$(filter nocheck,$(DEB_BUILD_OPTIONS)))
           # Code to run the package test suite.
   endif


4.9.2. "debian/rules" and "DEB_BUILD_PROFILES"
----------------------------------------------

If the "DEB_BUILD_PROFILES" environment variable is defined during the
build of a source package, it specifies which build profiles are
enabled. Its value is a space-separated, unordered list of enabled
build profile names. By default, no build profiles are enabled. The
following build profiles are standard:

"nocheck"
   This profile extends the meaning of the "nocheck" tag in
   "DEB_BUILD_OPTIONS" and must not be enabled unless combined with
   that tag. In addition to disabling build-time testing, it allows
   skipping the installation of dependencies required for those tests
   during the build. Note that enabling the profile or the tag must
   not functionally change the emitted binary packages and also must
   not change the set of binary packages produced. If tests happen to
   be installed into a binary package, it is recommended to add the
   "noinsttest" build profile.

"noinsttest"
   This profile disables the emission of binary packages consisting
   entirely of automated tests, manual tests, example/demo programs,
   and test tools. Other packages must not functionally change when
   this profile is enabled. Note that in many cases, it is only
   possible to drop such dependencies used for building when enabling
   both the "noinsttest" and the "nocheck" build profile at the same
   time.  Therefore such dependencies tend to be conditional to
   "<!nocheck> <!noinsttest>".

Commonly used but non-standard build profiles can be found in the
Build Profile Spec.

The following makefile snippet is an example of how to enable Python
support for all builds except when the package is built with the
"nopython" build profile active.

   ifneq ($(filter nopython,$(DEB_BUILD_PROFILES)),)
       # nopython build profile was activated -- disable python
       CONFIGURE_SWITCHES += --disable-python
   else
       CONFIGURE_SWITCHES += --enable-python
   endif

Alternatively, one may defer the evaluation of restriction formulas in
general (including architecture restrictions) to "debhelper".

   ifneq ($(filter foo,$(shell dh_listpackages)),)
       # foo is being built
       CONFIGURE_SWITCHES += --enable-foo
   else
       CONFIGURE_SWITCHES += --disable-foo
   endif


4.9.3. "debian/rules" and "Rules-Requires-Root"
-----------------------------------------------

Depending on the value of the Rules-Requires-Root field, the package
builder (e.g. dpkg-buildpackage) may run the "debian/rules" target as
an unprivileged user and provide a *gain root command*.  This command
allows the "debian/rules" target to run particular subcommands under
(fake)root.

The *gain root command* is passed to the build script via the
"DEB_GAIN_ROOT_CMD" environment variable.  The contents of this
variable is a space separated list, the first entry of which is the
command, and the proceeding entries of which are arguments to the
command.  The *gain root command* must be available via PATH.  The
*gain root command* must not rely on shell features because it will
not necessarily be invoked via a shell.

The *gain root command* must not run interactively, including
prompting for any user input.  It must be possible to prepend the
*gain root command* to an existing command and its arguments, without
needing to alter or quote the existing command and its arguments.
Furthermore, the *gain root command* must preserve all environment
variables without the caller having to explicitly request any
preservation.

The following are examples of valid gain root commands (in syntax of
sh), assuming the tools used are available and properly configured:

   # Command "sudo", with arguments "-nE" and "--"
   export DEB_GAIN_ROOT_CMD='sudo -nE --'
   # Command "fakeroot" with the single argument "--"
   export DEB_GAIN_ROOT_CMD='fakeroot --'

Examples of valid use of the *gain root command*:

   # sh-syntax (assumes set -e semantics for error handling)
   $DEB_GAIN_ROOT_CMD some-cmd --which-requires-root

   # perl
   my @cmd = ('some-cmd', '--which-requires-root');
   unshift(@cmd, split(' ', $ENV{DEB_GAIN_ROOT_CMD})) if $ENV{DEB_GAIN_ROOT_CMD};
   system(@cmd) == 0 or die("@cmd failed");


4.10. Variable substitutions: "debian/substvars"
================================================

When "dpkg-gencontrol" generates binary package control files
("DEBIAN/control"), it performs variable substitutions on its output
just before writing it. Variable substitutions have the form
"${variable}". The optional file "debian/substvars" contains variable
substitutions to be used; variables can also be set directly from
"debian/rules" using the "-V" option to the source packaging commands,
and certain predefined variables are also available.

The "debian/substvars" file is usually generated and modified
dynamically by "debian/rules" targets, in which case it must be
removed by the "clean" target.

See *deb-substvars(5)* for full details about source variable
substitutions, including the format of "debian/substvars".


4.11. Upstream source location: "debian/watch"
==============================================

This is a configuration file for the "uscan" utility which defines how
to automatically scan ftp or http sites for newly available updates of
the package. This is also used by some Debian QA tools to help with
quality control and maintenance of the distribution as a whole. If the
upstream source of the package is available via a mechaism that
"uscan" understands, including this configuration file is recommended.

If the upstream maintainer of the software provides OpenPGP signatures
for new releases, including the information required for "uscan" to
verify signatures for new upstream releases is also recommended. To do
this, use the "pgpsigurlmangle" option in "debian/watch" to specify
the location of the upstream signature, and include the key or keys
used to sign upstream releases in the Debian source package as
"debian/upstream/signing-key.asc".

For more information about "uscan" and these options, including how to
generate the file containing upstream signing keys, see *uscan(1)*.


4.12. Generated files list: "debian/files"
==========================================

This file is not a permanent part of the source tree; it is used while
building packages to record which files are being generated. "dpkg-
genchanges" uses it when it generates a ".changes" file.

It should not exist in a shipped source package, and so it (and any
backup files or temporary files such as "files.new")  [15] should be
removed by the "clean" target. It may also be wise to ensure a fresh
start by emptying or removing it at the start of the "binary" target.

When "dpkg-gencontrol" is run for a binary package, it adds an entry
to "debian/files" for the ".deb" file that will be created when "dpkg-
deb --build" is run for that binary package. So for most packages all
that needs to be done with this file is to delete it in the "clean"
target.

If a package upload includes files besides the source package and any
binary packages whose control files were made with "dpkg-gencontrol"
then they should be placed in the parent of the package's top-level
directory and "dpkg-distaddfile" should be called to add the file to
the list in "debian/files".


4.13. Embedded code copies
==========================

Some software packages include in their distribution convenience
copies of code from other software packages, generally so that users
compiling from source don't have to download multiple packages. Debian
packages should not make use of these convenience copies unless the
included package is explicitly intended to be used in this way.  [16]
If the included code is already in the Debian archive in the form of a
library, the Debian packaging should ensure that binary packages
reference the libraries already in Debian and the convenience copy is
not used. If the included code is not already in Debian, it should be
packaged separately as a prerequisite if possible.  [17]


4.14. Source package handling: "debian/README.source"
=====================================================

If running "dpkg-source -x" on a source package doesn't produce the
source of the package, ready for editing, and allow one to make
changes and run "dpkg-buildpackage" to produce a modified package
without taking any additional steps, creating a "debian/README.source"
documentation file is recommended. This file should explain how to do
all of the following:

1. Generate the fully patched source, in a form ready for editing,
   that would be built to create Debian packages. Doing this with a
   "patch" target in "debian/rules" is recommended; see Main building
   script: debian/rules.

2. Modify the source and save those modifications so that they will be
   applied when building the package.

3. Remove source modifications that are currently being applied when
   building the package.

4. Optionally, document what steps are necessary to upgrade the Debian
   source package to a new upstream version, if applicable.

This explanation should include specific commands and mention any
additional required Debian packages. It should not assume familiarity
with any specific Debian packaging system or patch management tools.

This explanation may refer to a documentation file installed by one of
the package's build dependencies provided that the referenced
documentation clearly explains these tasks and is not a general
reference manual.

"debian/README.source" may also include any other information that
would be helpful to someone modifying the source package. Even if the
package doesn't fit the above description, maintainers are encouraged
to document in a "debian/README.source" file any source package with a
particularly complex or unintuitive source layout or build system (for
example, a package that builds the same source multiple times to
generate different binary packages).


4.15. Reproducibility
=====================

Packages should build reproducibly, which for the purposes of this
document [18] means that given

* a version of a source package unpacked at a given path;

* a set of versions of installed build dependencies;

* a set of environment variable values;

* a build architecture; and

* a host architecture,

repeatedly building the source package for the build architecture on
any machine of the host architecture with those versions of the build
dependencies installed and exactly those environment variable values
set will produce bit-for-bit identical binary packages.

It is recommended that packages produce bit-for-bit identical binaries
even if most environment variables and build paths are varied.  It is
intended for this stricter standard to replace the above when it is
easier for packages to meet it.


4.16. Missing sources: "debian/missing-sources"
===============================================

Sometimes upstream does not include the source code for some files in
the upstream tarball.  In order to satisfy the DFSG for packages in
"main" or "contrib", you should either:

1. repack the upstream tarball to include those sources; or

2. include a copy of the sources in the "debian/missing-sources"
   directory.

Package maintainers may optionally use the following convention to
organize the contents of "debian/missing-sources": for a sourceless
file "foo" in the subdirectory "bar" of the upstream tarball, where
the source of "foo" has extension "baz", place the source at "debian
/missing-sources/bar/foo.baz". For example, according to this
convention, the C source code of an executable "checksum/util" would
be located at "debian/missing-sources/checksum/util.c".


4.17. Vendor-specific patch series
==================================

Packages in the Debian archive using the 3.0 (quilt) source package
format must not contain a non-default series file.  That is, there
must not exist a file "debian/patches/foo.series" for any "foo".

[1] Rationale:

    * This allows maintaining the list separately from the policy
      documents (the list does not need the kind of control that the
      policy documents do).

    * Having a separate package allows one to install the build-
      essential packages on a machine, as well as allowing other
      packages such as tasks to require installation of the build-
      essential packages using the depends relation.

    * The separate package allows bug reports against the list to be
      categorized separately from the policy management process in the
      BTS.

[2] The reason for this is that dependencies change, and you should
    list all those packages, and *only* those packages that *you* need
    directly. What others need is their business. For example, if you
    only link against "libimlib", you will need to build-depend on
    libimlib2-dev but not against any "libjpeg*" packages, even though
    "libimlib2-dev" currently depends on them: installation of
    libimlib2-dev will automatically ensure that all of its run-time
    dependencies are satisfied.

[3] Mistakes in changelogs are usually best rectified by making a new
    changelog entry rather than "rewriting history" by editing old
    changelog entries.

[4] Although there is nothing stopping an author who is also the
    Debian maintainer from using this changelog for all their changes,
    it will have to be renamed if the Debian and upstream maintainers
    become different people. In such a case, however, it might be
    better to maintain the package as a non-native package.

[5] To be precise, the string should match the following Perl regular
    expression:

       /closes:\s*(?:bug)?\#?\s?\d+(?:,\s*(?:bug)?\#?\s?\d+)*/i

    That is: The string should consist of the word "closes:" followed
    by a comma-separated list of bug numbers. Bug numbers may be
    preceded by the word "bug" and/or a "#" sign, as in "Closes: 42,
    bug#43, #44, bug 45".

    The list of bug numbers may span multiple lines.

    All of the bug numbers listed will be closed by the archive
    maintenance software ("dak") using the version of the changelog
    entry.

    The words "closes:" and "bug" are not case sensitive.

[6] In the case of a sponsored upload, the uploader signs the files,
    but the changelog maintainer name and address are those of the
    person who prepared this release. If the preparer of the release
    is not one of the usual maintainers of the package (as listed in
    the Maintainer or Uploaders control fields of the package), the
    first line of the changelog is conventionally used to explain why
    a non-maintainer is uploading the package. The Debian Developer's
    Reference (see Related documents) documents the conventions used.

[7] This is the same as the format generated by "date -R".

[8] The rationale is that there is some information conveyed by
    knowing the age of the file, for example, you could recognize that
    some documentation is very old by looking at the modification
    time, so it would be nice if the modification time of the upstream
    source would be preserved.

[9] Setgid directories are allowed.

[10] Another common way to do this is for "build" to depend on "build-
     stamp" and to do nothing else, and for the "build-stamp" target
     to do the building and to "touch build-stamp" on completion. This
     is especially useful if the build routine creates a file or
     directory called "build"; in such a case, "build" will need to be
     listed as a phony target (i.e., as a dependency of the ".PHONY"
     target). See the documentation of "make" for more information on
     phony targets.

[11] This split allows binary-only builds to not install the
     dependencies required for the "build-indep" target and skip any
     resource-intensive build tasks that are only required when
     building architecture-independent binary packages.

[12] The "fakeroot" package often allows one to build a package
     correctly even without being root.

[13] Some packages support any delimiter, but whitespace is the
     easiest to parse inside a makefile and avoids ambiguity with flag
     values that contain commas.

[14] Packages built with "make" can often implement this by passing
     the "-j"n option to "make".

[15] "files.new" is used as a temporary file by "dpkg-gencontrol" and
     "dpkg-distaddfile" - they write a new version of "files" here
     before renaming it, to avoid leaving a corrupted copy if an error
     occurs.

[16] For example, parts of the GNU build system work like this.

[17] Having multiple copies of the same code in Debian is inefficient,
     often creates either static linking or shared library conflicts,
     and, most importantly, increases the difficulty of handling
     security vulnerabilities in the duplicated code.

[18] This is Debian's precisification of the reproducible-builds.org
     definition.



5. Control files and their fields
*********************************

The package management system manipulates data represented in a common
format, known as *control data*, stored in *control files*. Control
files are used for source packages, binary packages and the ".changes"
files which control the installation of uploaded files.  [1]


5.1. Syntax of control files
============================

A control file consists of one or more stanzas of fields.  [2] The
stanzas are separated by empty lines. Parsers may accept lines
consisting solely of spaces and tabs as stanza separators, but control
files should use empty lines. Some control files allow only one
stanza; others allow several, in which case each stanza usually refers
to a different package. (For example, in source packages, the first
stanza refers to the source package, and later stanzas refer to binary
packages generated from the source.) The ordering of the stanzas in
control files is significant.

Each stanza consists of a series of data fields. Each field consists
of the field name followed by a colon and then the data/value
associated with that field. The field name is composed of US-ASCII
characters excluding control characters, space, and colon (i.e.,
characters in the ranges U+0021 ("!") through U+0039 ("9"), and U+003B
(";") through U+007E ("~"), inclusive). Field names must not begin
with the comment character (U+0023 "#"), nor with the hyphen character
(U+002D "-").

The field ends at the end of the line or at the end of the last
continuation line (see below). Horizontal whitespace (spaces and tabs)
may occur immediately before or after the value and is ignored there;
it is conventional to put a single space after the colon. For example,
a field might be:

   Package: libc6

the field name is "Package" and the field value "libc6".

Empty field values are only permitted in source package template
control files ("debian/control"). Such fields are ignored.

A stanza must not contain more than one instance of a particular field
name.

There are three types of fields:

simple
   The field, including its value, must be a single line. Folding of
   the field is not permitted. This is the default field type if the
   definition of the field does not specify a different type.

folded
   The value of a folded field is a logical line that may span several
   lines. The lines after the first are called continuation lines and
   must start with a space or a tab. Whitespace, including any
   newlines, is not significant in the field values of folded fields.
   [3]

multiline
   The value of a multiline field may comprise multiple continuation
   lines. The first line of the value, the part on the same line as
   the field name, often has special significance or may have to be
   empty. Other lines are added following the same syntax as the
   continuation lines of the folded fields. Whitespace, including
   newlines, is significant in the values of multiline fields.

Whitespace must not appear inside names (of packages, architectures,
files or anything else) or version numbers, or between the characters
of multi-character version relationships.

The presence and purpose of a field, and the syntax of its value, may
differ between types of control files.

Field names are not case-sensitive, but it is usual to capitalize the
field names using mixed case as shown below. Field values are case-
sensitive unless the description of the field says otherwise.

Stanza separators (empty lines), and lines consisting only of U+0020
SPACE and U+0009 TAB, are not allowed within field values or between
fields. Empty lines in field values are usually escaped by
representing them by a U+0020 SPACE followed by a U+002E (".").

Lines starting with U+0023 ("#"), without any preceding whitespace,
are comment lines that are only permitted in source package control
files ("debian/control"). These comment lines are ignored, even
between two continuation lines. They do not end logical lines.

All control files must be encoded in UTF-8.


5.2. Debian source package template control files -- "debian/control"
=====================================================================

The "debian/control" file contains the most vital (and version-
independent) information about the source package and about the binary
packages it creates.

The first stanza of the control file contains information about the
source package in general. The subsequent stanzas each describe a
binary package that the source tree builds. Each binary package built
from this source package has a corresponding stanza, except for any
automatically-generated debug packages that do not require one.

The fields in the source package stanza (the first one) are:

* Source (mandatory)

* Maintainer (mandatory)

* Uploaders

* Section (recommended)

* Priority

* Build-Depends et al

* Standards-Version (mandatory)

* Homepage

* Version Control System (VCS) fields

* Testsuite

* Rules-Requires-Root

The fields in the binary package stanzas are:

* Package (mandatory)

* Architecture (mandatory)

* Section (recommended)

* Priority

* Essential

* Depends et al

* Description (mandatory)

* Homepage

* Built-Using

* Package-Type

* *Build-Profiles*

The syntax and semantics of the fields are described below.

These fields are used by "dpkg-gencontrol" to generate control files
for binary packages (see below), by "dpkg-genchanges" to generate the
".changes" file to accompany the upload, and by "dpkg-source" when it
creates the ".dsc" source control file as part of a source archive.
Some fields are folded in "debian/control", but not in any other
control file. These tools are responsible for removing the line breaks
from such fields when using fields from "debian/control" to generate
other control files. They are also responsible for discarding empty
fields.

The fields here may contain variable references - their values will be
substituted by "dpkg-gencontrol", "dpkg-genchanges" or "dpkg-source"
when they generate output control files. See Variable substitutions:
debian/substvars for details.


5.3. Debian binary package control files -- "DEBIAN/control"
============================================================

The "DEBIAN/control" file contains the most vital (and version-
dependent) information about a binary package. It consists of a single
stanza.

The fields in this file are:

* Package (mandatory)

* Source

* Version (mandatory)

* Section (recommended)

* Priority (recommended)

* Architecture (mandatory)

* Essential

* Depends et al

* Installed-Size

* Maintainer (mandatory)

* Description (mandatory)

* Homepage

* Built-Using


5.4. Debian source package control files -- ".dsc"
==================================================

This file consists of a single stanza, possibly surrounded by an
OpenPGP signature. The fields of that stanza are listed below. Their
syntax is described above, in Syntax of control files.

* Format (mandatory)

* Source (mandatory)

* Binary

* Architecture

* Version (mandatory)

* Maintainer (mandatory)

* Uploaders

* Homepage

* Version Control System (VCS) fields

* Testsuite

* Dgit

* Git-Tag-Tagger

* Git-Tag-Info

* Standards-Version (mandatory)

* Build-Depends et al

* Package-List (recommended)

* Checksums-Sha1 and Checksums-Sha256 (mandatory)

* Files (mandatory)

The Debian source package control file is generated by "dpkg-source"
when it builds the source archive, from other files in the source
package, described above. When unpacking, it is checked against the
files and directories in the other parts of the source package.


5.5. Debian upload changes control files -- ".changes"
======================================================

The ".changes" files are used by the Debian archive maintenance
software to process updates to packages. They consist of a single
stanza, possibly surrounded by an OpenPGP signature. That stanza
contains information from the "debian/control" file and other data
about the source package gathered via "debian/changelog" and
"debian/rules".

".changes" files have a format version that is incremented whenever
the documented fields or their meaning change. This document describes
format 1.8.

The fields in this file are:

* Format (mandatory)

* Date (mandatory)

* Source (mandatory)

* Binary (mandatory in some cases)

* Architecture (mandatory)

* Version (mandatory)

* Distribution (mandatory)

* Urgency (recommended)

* Maintainer (mandatory)

* Changed-By

* Git-Tag-Tagger

* Git-Tag-Info

* Description (mandatory in some cases)

* Closes

* Changes (mandatory)

* Checksums-Sha1 and Checksums-Sha256 (mandatory)

* Files (mandatory)


5.6. List of fields
===================


5.6.1. "Source"
---------------

This field identifies the source package name.

In "debian/control" or a ".dsc" file, this field must contain only the
name of the source package.

In a binary package control file or a ".changes" file, the source
package name may be followed by a version number in parentheses.  [4]
This version number may be omitted (and is, by "dpkg-gencontrol") if
it has the same value as the "Version" field of the binary package in
question. The field itself may be omitted from a binary package
control file when the source package has the same name and version as
the binary package.

Package names (both source and binary, see Package) must consist only
of lower case letters ("a-z"), digits ("0-9"), plus ("+") and minus
("-") signs, and periods ("."). They must be at least two characters
long and must start with an alphanumeric character.


5.6.2. "Maintainer"
-------------------

The package maintainer's name and email address. The name must come
first, then the email address inside angle brackets "<>" (in RFC822
format).

If the maintainer's name contains a full stop then the whole field
will not work directly as an email address due to a misfeature in the
syntax specified in RFC822; a program using this field as an address
must check for this and correct the problem if necessary (for example
by putting the name in round brackets and moving it to the end, and
bringing the email address forward).

See The maintainer of a package for additional requirements and
information about package maintainers.


5.6.3. "Uploaders"
------------------

List of the names and email addresses of co-maintainers of the
package, if any. If the package has other maintainers besides the one
named in the Maintainer field, their names and email addresses should
be listed here. The format of each entry is the same as that of the
Maintainer field, and multiple entries must be comma separated.

This is normally an optional field, but if the "Maintainer" control
field names a group of people and a shared email address, the
"Uploaders" field must be present and must contain at least one human
with their personal email address.

The Uploaders field in "debian/control" can be folded.


5.6.4. "Changed-By"
-------------------

The name and email address of the person who prepared this version of
the package, usually a maintainer. The syntax is the same as for the
Maintainer field.


5.6.5. "Section"
----------------

This field specifies an application area into which the package has
been classified. See Sections.

When it appears in the "debian/control" file, it gives the value for
the subfield of the same name in the "Files" field of the ".changes"
file. It also gives the default for the same field in the binary
packages.


5.6.6. "Priority"
-----------------

This field represents how important it is that the user have the
package installed. See Priorities.

When it appears in the "debian/control" file, it gives the value for
the subfield of the same name in the "Files" field of the ".changes"
file. It also gives the default for the same field in the binary
packages.


5.6.7. "Package"
----------------

The name of the binary package.

Binary package names must follow the same syntax and restrictions as
source package names. See Source for the details.


5.6.8. "Architecture"
---------------------

Depending on context and the control file used, the "Architecture"
field can include the following sets of values:

* A unique single word identifying a Debian machine architecture as
  described in Architecture specification strings.

* An architecture wildcard identifying a set of Debian machine
  architectures, see Architecture wildcards. "any" matches all Debian
  machine architectures and is the most frequently used.

* "all", which indicates an architecture-independent package.

* "source", which indicates a source package.

In the main "debian/control" file in the source package, this field
may contain the special value "all", the special architecture wildcard
"any", or a list of specific and wildcard architectures separated by
spaces. If "all" or "any" appears, that value must be the entire
contents of the field. Most packages will use either "all" or "any".

Specifying a specific list of architectures indicates that the source
will build an architecture-dependent package only on architectures
included in the list. Specifying a list of architecture wildcards
indicates that the source will build an architecture-dependent package
on only those architectures that match any of the specified
architecture wildcards. Specifying a list of architectures or
architecture wildcards other than "any" is for the minority of cases
where a program is not portable or is not useful on some
architectures. Where possible, the program should be made portable
instead.

In the Debian source package control file ".dsc", this field contains
a list of architectures and architecture wildcards separated by
spaces. When the list contains the architecture wildcard "any", the
only other value allowed in the list is "all".

The list may include (or consist solely of) the special value "all".
In other words, in ".dsc" files unlike the "debian/control", "all" may
occur in combination with specific architectures. The "Architecture"
field in the Debian source package control file ".dsc" is generally
constructed from the "Architecture" fields in the "debian/control" in
the source package.

Specifying only "any" indicates that the source package isn't
dependent on any particular architecture and should compile fine on
any one. The produced binary package(s) will be specific to whatever
the current build architecture is.

Specifying only "all" indicates that the source package will only
build architecture-independent packages.

Specifying "any all" indicates that the source package isn't dependent
on any particular architecture. The set of produced binary packages
will include at least one architecture-dependent package and one
architecture-independent package.

Specifying a list of architectures or architecture wildcards indicates
that the source will build an architecture-dependent package, and will
only work correctly on the listed or matching architectures. If the
source package also builds at least one architecture-independent
package, "all" will also be included in the list.

In a ".changes" file, the "Architecture" field lists the
architecture(s) of the package(s) currently being uploaded. This will
be a list; if the source for the package is also being uploaded, the
special entry "source" is also present. "all" will be present if any
architecture-independent packages are being uploaded. Architecture
wildcards such as "any" must never occur in the "Architecture" field
in the ".changes" file.

See Main building script: debian/rules for information on how to get
the architecture for the build process.


5.6.9. "Essential"
------------------

This is a boolean field which may occur only in the control file of a
binary package or in a binary package stanza of a source package
template control file.

If set to "yes" then the package management system will refuse to
remove the package (upgrading and replacing it is still possible). The
other possible value is "no", which is the same as not having the
field at all.


5.6.10. Package interrelationship fields: "Depends", "Pre-Depends", "Recommends", "Suggests", "Breaks", "Conflicts", "Provides", "Replaces", "Enhances"
-------------------------------------------------------------------------------------------------------------------------------------------------------

These fields describe the package's relationships with other packages.
Their syntax and semantics are described in Declaring relationships
between packages.


5.6.11. "Standards-Version"
---------------------------

The most recent version of the standards (the policy manual and
associated texts) with which the package complies.  See Standards
conformance.

The version number has four components: major and minor version number
and major and minor patch level. When the standards change in a way
that requires every package to change the major number will be
changed. Significant changes that will require work in many packages
will be signaled by a change to the minor number. The major patch
level will be changed for any change to the meaning of the standards,
however small; the minor patch level will be changed when only
cosmetic, typographical or other edits are made which neither change
the meaning of the document nor affect the contents of packages.

Thus only the first three components of the policy version are
significant in the *Standards-Version* control field, and so either
these three components or all four components may be specified. [5]

udebs and source packages that only produce udebs do not use
"Standards-Version".


5.6.12. "Version"
-----------------

The version number of a package. The format is:
"[epoch:]upstream_version[-debian_revision]".

The three components here are:

"epoch"
   This is a single (generally small) unsigned integer. It may be
   omitted, in which case zero is assumed.

   Epochs can help when the upstream version numbering scheme changes,
   but they must be used with care.  You should not change the epoch,
   even in experimental, without getting consensus on debian-devel
   first.

"upstream_version"
   This is the main part of the version number. It is usually the
   version number of the original ("upstream") package from which the
   ".deb" file has been made, if this is applicable. Usually this will
   be in the same format as that specified by the upstream author(s);
   however, it may need to be reformatted to fit into the package
   management system's format and comparison scheme.

   The comparison behavior of the package management system with
   respect to the "upstream_version" is described below. The
   "upstream_version" portion of the version number is mandatory.

   The "upstream_version" must contain only alphanumerics [6] and the
   characters "." "+" "-" "~" (full stop, plus, hyphen, tilde) and
   should start with a digit. If there is no "debian_revision" then
   hyphens are not allowed.

"debian_revision"
   This part of the version number specifies the version of the Debian
   package based on the upstream version. It must contain only
   alphanumerics and the characters "+" "." "~" (plus, full stop,
   tilde) and is compared in the same way as the "upstream_version"
   is.

   It is conventional to restart the "debian_revision" at "1" each
   time the "upstream_version" is increased.

   The package management system will break the version number apart
   at the last hyphen in the string (if there is one) to determine the
   "upstream_version" and "debian_revision". The absence of a
   "debian_revision" is equivalent to a "debian_revision" of "0".

   Presence of the "debian_revision" part indicates this package is a
   non-native package (see Source packages).  Absence indicates the
   package is a native package.

When comparing two version numbers, first the epoch of each are
compared, then the "upstream_version" if epoch is equal, and then
"debian_revision" if "upstream_version" is also equal. epoch is
compared numerically. The "upstream_version" and "debian_revision"
parts are compared by the package management system using the
following algorithm:

The strings are compared from left to right.

First the initial part of each string consisting entirely of non-digit
characters is determined. These two parts (one of which may be empty)
are compared lexically. If a difference is found it is returned. The
lexical comparison is a comparison of ASCII values modified so that
all the letters sort earlier than all the non-letters and so that a
tilde sorts before anything, even the end of a part. For example, the
following parts are in sorted order from earliest to latest: "~~",
"~~a", "~", the empty part, "a". [7]

Then the initial part of the remainder of each string which consists
entirely of digit characters is determined. The numerical values of
these two parts are compared, and any difference found is returned as
the result of the comparison. For these purposes an empty string
(which can only occur at the end of one or both version strings being
compared) counts as zero.

These two steps (comparing and removing initial non-digit strings and
initial digit strings) are repeated until a difference is found or
both strings are exhausted.


5.6.12.1. Epochs should be used sparingly
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Note that the purpose of epochs is to cope with situations where the
upstream version numbering scheme changes and to allow us to leave
behind serious mistakes. If you think that increasing the epoch is the
right solution, you should consult debian-devel and get consensus
before doing so (even in experimental).

Epochs should not be used when a package needs to be rolled back. In
that case, use the "+really" convention: for example, if you uploaded
"2.3-3" and now you need to go backwards to upstream 2.2, call your
reverting upload something like "2.3+really2.2-1". Eventually, when we
upload upstream 2.4, the "+really" part can go away.

Epochs are also not intended to cope with version numbers containing
strings of letters which the package management system cannot
interpret (such as "ALPHA" or "pre-"), or with silly orderings.  [8]


5.6.12.2. Special version conventions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following special version numbering conventions are used in the
Debian archive:

* The absence of "debian_revision", and therefore of a hyphen in the
  version number, indicates that the package is native.

* The presence of "+really" in the "upstream_version" component
  indicates that a newer upstream version has been rolled back to an
  older upstream version.  The part of the "upstream_version"
  component following "+really" is the true upstream version.  See
  Epochs should be used sparingly for an example of when this is used.

Non-maintainer uploads:

* "debian_revision" components ending in "." (period) followed by a
  number indicate this version of the non-native package was uploaded
  by someone other than the maintainer (an NMU or non-maintainer
  upload).  This is used for a upload including a source package; for
  uploads of only binary packages without source changes, see the
  binary NMU convention below.

* "upstream_version" components in native packages ending in "+nmu"
  followed by a number indicate an NMU of a native package.  As with
  the convention for non-native packages, this is used for an upload
  including a source package, not for uploads of only binary packages
  without source changes.

* "upstream_version" components in native packages or
  "debian_revision" components in non-native packages ending in "+b"
  followed by a number indicate a binary NMU: an upload of a binary
  package without any source changes and hence without any
  corresponding source package upload or version change.

Stable updates:

* "debian_revision" components in non-native packages ending in
  "debNuX" also indicate a stable update.  Either "~" or "+" will be
  used before this string depending on the details of the update.  "N"
  is the major version number of the Debian stable release to which
  the package was uploaded, and "X" is a number, starting at 1, that
  is increased for each stable upload of this package.

  There are three cases for non-native packages:

  1. For stable updates that use the same upstream version, the
     "debian_revision" component will end in "+debNuX".  The portion
     of the version before that string is the original package version
     in the stable release.

  2. For stable updates to a new upstream version that is based on a
     newer unstable package, the "debian_revision" component will end
     in "~debNuX".  The portion before that string will be the
     unstable version on which the package is based.

  3. If a stable update is based on a new upstream version but is not
     based on a newer unstable package, the convention is to form the
     version number by taking the upstream version, appending "-0",
     and then appending "+debNuX" (so the "debian_revision" component
     will be "0+debNuX").

  In all cases, these versions are chosen so that they will sort
  earlier than a subsequent unstable package of the same upstream
  version and thus that the stable package will upgrade to a newer
  version during a subsequent system upgrade.

  For example, suppose Debian 10 released with a package with version
  "1.4-5".  If that package later receives a stable update in Debian
  10 that uses the same upstream version, the first update would have
  the version "1.4-5+deb10u1".  A subsequent update would have version
  "1.4-5+deb10u2".

  If instead the package receives a stable update based on a "1.5-1"
  unstable package, the first such stable update would have the
  version "1.5-1~deb10u1" and a subsequent update would have the
  version "1.5-1~deb10u2".

  If there were no unstable "1.5-1" package, but there were a stable
  update to an upstream 1.5 release, the first such stable update
  would have the version "1.5-0+deb10u1".

* "upstream_version" components in native packages ending in "+debNuX"
  indicate a stable update.  This is a version of the package uploaded
  directly to a stable release, and the version is chosen to sort
  before any later version of the package uploaded to Debian's
  unstable or a later stable distribution.  As with non-native
  packages, "N" is the major version number of the Debian stable
  release to which the package was uploaded, and "X" is a number,
  starting at 1, that is increased for each stable upload of this
  package.

  For example, suppose Debian 10 released with a package with version
  "1.4".  The first stable update of that package would have the
  version "1.4+deb10u1", and a subsequent update would have the
  version "1.4+deb10u2".  These versions are chosen to sort before
  "1.5" (the next unstable version) or "1.4+deb11u1" (a stable update
  to a subsequent Debian 11 release).

Backports:

* "upstream_version" components in native packages or
  "debian_revision" components in non-native packages ending in
  "~bpoNuX" indicate a backport of a version of the package to an
  older stable release.  The part of the version before "~bpo" is the
  version of the package being backported, "N" is the major version
  number of the Debian stable release to which the package was
  backported, and "X" is a number, starting at 1, that is increased
  for each revision of the backport of that package version.  The
  rationale is the same as for stable updates, with the additional
  goal of ensuring a backported version sorts earlier than a stable
  update with the same upstream version.

  Be aware that the stable update and backport conventions can stack.
  If, for example, Debian 10 contains a package with version
  "1.4-5+deb10u1" and that package is backported to Debian 9, the
  version of the Debian 9 backport would be "1.4-5+deb10u1~bpo9u1"
  (although this scenario is rare).

This list of version conventions is not exhaustive.


5.6.13. "Description"
---------------------

In a source template control file or binary control file, the
"Description" field contains a description of the binary package,
consisting of two parts, the synopsis or the short description, and
the long description. It is a multiline field with the following
format:

   Description: single line synopsis
    extended description over several lines

The lines in the extended description can have these formats:

* Those starting with a single space are part of a paragraph.
  Successive lines of this form will be word-wrapped when displayed.
  The leading space will usually be stripped off. The line must
  contain at least one non-whitespace character.

* Those starting with two or more spaces. These will be displayed
  verbatim. If the display cannot be panned horizontally, the
  displaying program will line wrap them "hard" (i.e., without taking
  account of word breaks). If it can they will be allowed to trail off
  to the right. None, one or two initial spaces may be deleted, but
  the number of spaces deleted from each line will be the same (so
  that you can have indenting work correctly, for example). The line
  must contain at least one non-whitespace character.

* Those containing a single space followed by a single full stop
  character. These are rendered as blank lines. This is the *only* way
  to get a blank line.  [9]

* Those containing a space, a full stop and some more characters.
  These are for future expansion. Do not use them.

Do not use tab characters. Their effect is not predictable.

See The description of a package for further information on this.

In a ".changes" file, the "Description" field contains a summary of
the descriptions of the binary packages being uploaded. If no binary
packages are being uploaded, this field will not be present.

When used inside a ".changes" file, the "Description" field has a
different format than in source or binary control files. It is a
multiline field with one line per binary package. The first line of
the field value (the part on the same line as "Description:") is
always empty. Each subsequent line is indented by one space and
contains the name of a binary package, a space, a hyphen ("-"), a
space, and the short description line from that package.


5.6.14. "Distribution"
----------------------

In a ".changes" file or parsed changelog output this contains the
(space-separated) name(s) of the distribution(s) where this version of
the package should be installed. Valid distributions are determined by
the archive maintainers.  [10] The Debian archive software only
supports listing a single distribution. Migration of packages to other
distributions is handled outside of the upload process.


5.6.15. "Date"
--------------

This field includes the date the package was built or last edited. It
must be in the same format as the date in a "debian/changelog" entry.

The value of this field is usually extracted from the
"debian/changelog" file - see Debian changelog: debian/changelog).


5.6.16. "Format"
----------------

In ".changes" files, this field declares the format version of that
file. The syntax of the field value is the same as that of a package
version number except that no epoch or Debian revision is allowed. The
format described in this document is 1.8.

In ".dsc" Debian source control files, this field declares the format
of the source package. The field value is used by programs acting on a
source package to interpret the list of files in the source package
and determine how to unpack it. The syntax of the field value is a
numeric major revision, a period, a numeric minor revision, and then
an optional subtype after whitespace, which if specified is an
alphanumeric word in parentheses. The subtype is optional in the
syntax but may be mandatory for particular source format revisions.
[11]


5.6.17. "Urgency"
-----------------

This is a description of how important it is to upgrade to this
version from previous ones. It consists of a single keyword taking one
of the values "low", "medium", "high", "emergency", or "critical" [12]
(not case-sensitive) followed by an optional commentary (separated by
a space) which is usually in parentheses. For example:

   Urgency: low (HIGH for users of diversions)

The value of this field is usually extracted from the
"debian/changelog" file - see Debian changelog: debian/changelog.


5.6.18. "Changes"
-----------------

This multiline field contains the human-readable changes data,
describing the differences between the last version and the current
one.

The first line of the field value (the part on the same line as
"Changes:") is always empty. The content of the field is expressed as
continuation lines, with each line indented by at least one space.
Blank lines must be represented by a line consisting only of a space
and a full stop (".").

The value of this field is usually extracted from the
"debian/changelog" file - see Debian changelog: debian/changelog.

Each version's change information should be preceded by a "title" line
giving at least the version, distribution(s) and urgency, in a human-
readable way.

If data from several versions is being returned the entry for the most
recent version should be returned first, and entries should be
separated by the representation of a blank line (the "title" line may
also be followed by the representation of a blank line).


5.6.19. "Binary"
----------------

This folded field is a list of binary packages. Its syntax and meaning
varies depending on the control file in which it appears.

When it appears in the ".dsc" file, it lists binary packages which a
source package can produce, separated by commas [13]. The source
package does not necessarily produce all of these binary packages for
every architecture. The source control file doesn't contain details of
which architectures are appropriate for which of the binary packages.

When it appears in a ".changes" file, it lists the names of the binary
packages being uploaded, separated by whitespace (not commas). If no
binary packages are being uploaded, this field will not be present.


5.6.20. "Installed-Size"
------------------------

This field appears in the binary package control files, and in the
"Packages" files. It gives an estimate of the total amount of disk
space required to install the named package. Actual installed size may
vary based on block size, file system properties, or actions taken by
package maintainer scripts.

The disk space is given as the accumulated size of each regular file
and symlink rounded to 1 KiB used units, and a baseline of 1 KiB for
any other filesystem object type.


5.6.21. "Files"
---------------

This field contains a list of files with information about each one.
The exact information and syntax varies with the context.

In all cases, "Files" is a multiline field. The first line of the
field value (the part on the same line as "Files:") is always empty.
The content of the field is expressed as continuation lines, one line
per file. Each line must be indented by one space and contain a number
of sub-fields, separated by spaces, as described below.

In the ".dsc" file, each line contains the MD5 checksum, size and
filename of the tar file and (if applicable) diff file which make up
the remainder of the source package.  [14] For example:

   Files:
    c6f698f19f2a2aa07dbb9bbda90a2754 571925 example_1.2.orig.tar.gz
    938512f08422f3509ff36f125f5873ba 6220 example_1.2-1.diff.gz

The exact forms of the filenames are described in Source packages as
archives.

In the ".changes" file this contains one line per file being uploaded.
Each line contains the MD5 checksum, size, section and priority and
the filename. For example:

   Files:
    4c31ab7bfc40d3cf49d7811987390357 1428 text extra example_1.2-1.dsc
    c6f698f19f2a2aa07dbb9bbda90a2754 571925 text extra example_1.2.orig.tar.gz
    938512f08422f3509ff36f125f5873ba 6220 text extra example_1.2-1.diff.gz
    7c98fe853b3bbb47a00e5cd129b6cb56 703542 text extra example_1.2-1_i386.deb

The section and priority are the values of the corresponding fields in
the source template control file. If no section or priority is
specified then "-" should be used, though section and priority values
must be specified for new packages to be installed properly.

The special value "byhand" for the section in a ".changes" file
indicates that the file in question is not an ordinary package file
and must be installed by hand by the distribution maintainers. If the
section is "byhand" the priority should be "-".

If a new Debian revision of a package is being shipped and no new
original source archive is being distributed the ".dsc" must still
contain the "Files" field entry for the original source archive
"package_upstream-version.orig.tar.gz", but the ".changes" file should
leave it out. In this case the original source archive on the
distribution site must match exactly, byte-for-byte, the original
source archive which was used to generate the ".dsc" file and diff
which are being uploaded.


5.6.22. "Closes"
----------------

A space-separated list of bug report numbers that the upload governed
by the ".changes" file closes.


5.6.23. "Homepage"
------------------

The URL of the web site for this package, preferably (when applicable)
the site from which the original source can be obtained and any
additional upstream documentation or information may be found. The
content of this field is a simple URL without any surrounding
characters such as "<>".


5.6.24. "Checksums-Sha1" and "Checksums-Sha256"
-----------------------------------------------

These multiline fields contain a list of files with a checksum and
size for each one. Both "Checksums-Sha1" and "Checksums-Sha256" have
the same syntax and differ only in the checksum algorithm used: SHA-1
for "Checksums-Sha1" and SHA-256 for "Checksums-Sha256".

"Checksums-Sha1" and "Checksums-Sha256" are multiline fields. The
first line of the field value (the part on the same line as
"Checksums-Sha1:" or "Checksums-Sha256:") is always empty. The content
of the field is expressed as continuation lines, one line per file.
Each line consists of the checksum, a space, the file size, a space,
and the file name. For example (from a ".changes" file):

   Checksums-Sha1:
    1f418afaa01464e63cc1ee8a66a05f0848bd155c 1276 example_1.0-1.dsc
    a0ed1456fad61116f868b1855530dbe948e20f06 171602 example_1.0.orig.tar.gz
    5e86ecf0671e113b63388dac81dd8d00e00ef298 6137 example_1.0-1.debian.tar.gz
    71a0ff7da0faaf608481195f9cf30974b142c183 548402 example_1.0-1_i386.deb
   Checksums-Sha256:
    ac9d57254f7e835bed299926fd51bf6f534597cc3fcc52db01c4bffedae81272 1276 example_1.0-1.dsc
    0d123be7f51e61c4bf15e5c492b484054be7e90f3081608a5517007bfb1fd128 171602 example_1.0.orig.tar.gz
    f54ae966a5f580571ae7d9ef5e1df0bd42d63e27cb505b27957351a495bc6288 6137 example_1.0-1.debian.tar.gz
    3bec05c03974fdecd11d020fc2e8250de8404867a8a2ce865160c250eb723664 548402 example_1.0-1_i386.deb

In the ".dsc" file, these fields list all files that make up the
source package. In the ".changes" file, these fields list all files
being uploaded. The list of files in these fields must match the list
of files in the "Files" field.


5.6.25. "DM-Upload-Allowed"
---------------------------

Obsolete, see below.


5.6.26. Version Control System (VCS) fields
-------------------------------------------

Debian source packages are increasingly developed using VCSs. The
purpose of the following fields is to indicate a publicly accessible
repository where the Debian source package is developed.

"Vcs-Browser"
   URL of a web interface for browsing the repository.

   Here is an example of the form the two values take for Debian's
   GitLab instance, Salsa:

      Vcs-Browser: https://salsa.debian.org/debian/grep
      Vcs-Git: https://salsa.debian.org/debian/grep.git

"Vcs-<type>"
   The field name identifies the VCS. The field's value uses the
   version control system's conventional syntax for describing
   repository locations and should be sufficient to locate the
   repository used for packaging. Ideally, it also locates the branch
   used for development of new versions of the Debian package.

   The following values for <type> are supported, with the
   corresponding VCS indicated in parentheses if it isn't obvious:

   * Arch

   * Bzr (Bazaar)

   * Cvs (CVS)

   * Darcs

   * Git

   * Hg (Mercurial)

   * Mtn (Monotone)

   * Svn (Subversion)

   In the case of Git, the value must have the following syntax:

      <url> [ " -b " <branch> ] [ " [" <path> "]" ]

   where the portions enclosed in brackets are optional and the
   portions enclosed in double quotes are literal strings.  "<url>"
   indicates the repository.  If the "<branch>" portion is present, it
   names a branch in the indicated repository.  If no branch is
   specified, the packaging should be on the default branch.  If the
   "<path>" portion is present, it specifies the relative path to the
   top of the packaging tree (the parent directory of the "debian"
   directory).  If no path is specified, it defaults to "." (the top
   level of the indicated repository and branch).

   For example:

      Vcs-Git: https://example.org/repo -b debian [p/package]

   indicates a subdirectory named "p/package" in the "debian" branch
   of the repository at "https://example.org/repo".

   In the case of Mercurial, the value must have the following syntax:

      <url> [ " -b " <branch> ]

   This is interpreted the same way as the Git syntax except a path
   within the repository is not supported.

   A package control file must not have more than one "Vcs-<type>"
   field.  If the package is maintained in multiple version control
   systems, the maintainer should specify the one that they would
   prefer other people to use as the basis for proposing changes to
   the package.

For both fields, any URLs given should use a scheme that provides
confidentiality ("https", for example, rather than "http" or "git") if
the VCS repository supports it.


5.6.27. "Package-List"
----------------------

Multiline field listing all the packages that can be built from the
source package, considering every architecture. The first line of the
field value is empty. Each one of the next lines describes one binary
package, by listing its name, type, section and priority separated by
spaces. Fifth and subsequent space-separated items may be present and
parsers must allow them. See the Package-Type field for a list of
package types.


5.6.28. "Package-Type"
----------------------

Simple field containing a word indicating the type of package: "deb"
for binary packages and "udeb" for micro binary packages. Other types
not defined here may be indicated. In source package template control
files, the "Package-Type" field should be omitted instead of giving it
a value of "deb", as this value is assumed for stanzas lacking this
field.


5.6.29. "Dgit"
--------------

Folded field containing a single git commit hash, presented in full,
followed optionally by whitespace and other data to be defined in
future extensions.

Declares that the source package corresponds exactly to a referenced
commit in a Git repository available at the canonical location called
*dgit-repos*, used by "dgit", a bidirectional gateway between the
Debian archive and Git. The commit is reachable from at least one
reference whose name matches "refs/dgit/*". See the manual page of
"dgit" for further details.


5.6.30. "Testsuite"
-------------------

Simple field containing a comma-separated list of values allowing test
execution environments to discover packages which provide tests.

This field is automatically added to Debian source control files
(".dsc") by "dpkg", with the value "autopkgtest", when a
"debian/tests/control" file is present in the source package. This
field may also be used in source package template control files
("debian/control") if needed in other situations.


5.6.31. "Rules-Requires-Root"
-----------------------------

Simple field that defines if the source package requires access to
root (or fakeroot) during selected targets in the Main building
script: debian/rules.

The field can consist of exactly one of the following three items:

   * "no" (default): Declares that neither root nor fakeroot is
     required. Package builders (e.g. dpkg-buildpackage) may choose to
     invoke any target in "debian/rules" with an unprivileged user.

   * "binary-targets" (previous default): Declares that the package
     will need the root (or fakeroot) when either of the "binary",
     "binary-arch" or "binary-indep" targets are called.  This is how
     every tool behaved before this field was defined.

   * A space separated list of keywords described below.  These
     keywords must always contain a forward slash, which sets them
     apart from the other possible values of "Rules-Requires-Root".
     When this list is provided, the builder must provide a "gain root
     command" (as defined in debian/rules and Rules-Requires-Root)
     *or* pretend that the value was set to "binary-targets", and both
     the builder and the package's "debian/rules" script must
     downgrade accordingly (see below).

The default depends on the dpkg-build-api level (see dpkg-build-
api(7)). If the dpkg-build-api level is undeclared, it is equivalent
to level 0.

If the package builder supports the "Rules-Requires-Root" field and
wants to enable the feature, then it must set the environment variable
"DEB_RULES_REQUIRES_ROOT" when invoking the package building script
"debian/rules".  The value of "DEB_RULES_REQUIRES_ROOT" should be one
of:

   * The value of "Rules-Requires-Root" if the builder can support
     that value.  The builder may trim unnecessary whitespace used to
     format the field for readability.

   * The value "binary-targets" if it cannot support the value of
     "Rules-Requires-Root".

A compliant builder may also leave "DEB_RULES_REQUIRES_ROOT" unset or
set it to "binary-targets" if it has been requested to test whether
the package it builds correctly implements the fall-back for legacy
builders.


5.6.31.1. Remarks
~~~~~~~~~~~~~~~~~

All packages and builders must support "binary-targets" as this was
the historical behaviour prior to the introduction of this field.

Any tool (particularly older versions of them) may be unaware of this
field and behave like the field was set to "binary-targets".  The
package build must gracefully cope with this and produce a
semantically equivalent result.

This field intentionally does not enable a package to request a true
root over fakeroot.


5.6.31.2. Definition of the keywords
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The keywords have the format "<namespace>/<case>", where:

   * "<namespace>" must consist entirely of printable ASCII characters
     except for any whitespace and the forward slash ("/").  It must
     consist of at least 2 characters.

   * "/" (between "<namespace>" and "<case>") is a single ASCII
     forward slash.

   * "<case>" must consist entirely of printable ASCII characters
     except for any whitespace.  It must consist of at least 2
     characters.

These keywords define where the package build script "debian/rules",
or the tools called by that script, will need access to root or
fakeroot.

In addition to the keywords defined in the next section, each tool or
package may define keywords within a namespace named after that tool
or package.  The package or tool is considered to own that namespace.

A tool is permitted to use the "gain root command" to do something
under (fake)root if and only if the tool defines an appropriate
keyword in its namespace, and the package lists that keyword in
"Rules-Requires-Root".

All tools must ignore keywords under namespaces they do not know or
own.  A tool may emit a warning, or abort with an error, if it finds
unknown keywords in namespaces it owns, but it is not required to do
this for all keywords in the namespace.


5.6.31.3. Provided keywords
~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following keywords are defined:

   * "dpkg/target-subcommand": declares that there exists a command
     that the "debian/rules" file must run under (fake)root

   * "dpkg/target/foo": declares that the additional, package-specific
     target "foo" (that is, not one of the targets specified in Main
     building script: debian/rules) must be run under (fake)root

This list is intentionally incomplete. You should consult the
documentation of the tool or package in question for which keywords it
defines and when they are needed.


5.6.32. "Git-Tag-Tagger"
------------------------

Name and e-mail address of the person who made the Git tag from which
this upload was generated (and to which it corresponds) in accordance
with the tagging protocol described in the *tag2upload(5)* manual page
and TAG2UPLOAD-DESIGN.txt. The syntax is the same as for the
Maintainer field. The values for the name and e-mail address originate
in the "tagger" line of the raw Git tag; they are transformed as
necessary to satisfy the field's syntax.

Uploads signed by an implemention of the tag2upload service must
include this field.  Uploads not generated in accordance with the
tag2upload protocol must not include this field.


5.6.33. "Git-Tag-Info"
----------------------

Other information about the Git tag from which this upload was
generated (and to which it corresponds) in accordance with the tagging
protocol described in the *tag2upload(5)* manual page and TAG2UPLOAD-
DESIGN.txt.

The value is of the form "tag=TAGOBJID fp=FINGERPRINT" where
"TAGOBJID" is the Git object ID of the Git annotated tag object, [15]
and "FINGERPRINT" is the fingerprint (in hexadecimal, without spaces)
of the PGP key used to sign the Git tag.  Other space-separated
"keyword=value" items may be introduced in the future, and users of
this field must ignore items with unknown keywords.

"FINGERPRINT" is taken from the first field of the "VALIDSIG" line
emitted by *gpgv(1)*, as specified in
"/usr/share/doc/gnupg/DETAILS.gz" from the "gnupg" package.  This will
generally be the fingerprint of the signing subkey, if one was used,
and the primary key's fingerprint otherwise.

The Git annotated tag object is obtainable from the *dgit-repos*
server, as described under "Dgit", above.

Uploads signed by an implemention of the tag2upload service must
include this field.  Uploads not generated in accordance with the
tag2upload protocol must not include this field.


5.6.34. "Multi-Arch"
--------------------

A Debian installation can combine packages from multiple
architectures. The "Multi-Arch" field enables individual packages to
declare their support for this feature, and influences the way
dependencies are handled.  It can be declared in binary package
sections of a source package template control file and in binary
package control files.  The permitted field values are "no" (default),
"foreign", "same" and "allowed". Their semantics are described in the
following sections.


5.6.34.1. "Multi-Arch: no"
~~~~~~~~~~~~~~~~~~~~~~~~~~

This means that a "Depends", "Pre-Depends", "Provides", "Recommends"
or "Suggests" relation between packages is satisfied only by packages
of the same architecture.  There is no effect on "Breaks", "Conflicts"
and "Replaces".  Furthermore, multiple instances of a package with the
same name but different architectures cannot be installed at the same
time.  Architecture-independent packages are treated as though they
had the architecture value of the installed "dpkg" package.

Note that, due to limitations in the archive management software, this
value cannot currently be specified explicitly in binary package
control files.  Instead, the field needs to be absent in order to
imply its default value and "debhelper" discards it when transforming
a source package control template.


5.6.34.2. "Multi-Arch: foreign"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This means that the interfaces the package provides are independent of
its architecture, and that it therefore satisfies dependencies on a
package of this name regardless of the architecture of the package
declaring the dependency. Any virtual packages provided (see Virtual
packages - Provides) inherit this property.

There are five main areas that can contribute to the interface of a
package. If any of them provides an architecture-dependent interface,
a package must not be marked with "Multi-Arch: foreign". Note that
architecture-independent packages can reasonably provide architecture-
dependent interfaces and therefore architecture-independent packages
are not implicitly treated as "Multi-Arch: foreign".

* The installed files of a package: Architecture-dependent packages
  may install different sets of files or files with different content
  for different architectures. These differences may contribute to the
  interface (e.g. an endianness-dependent database file).  For
  architecture-independent binary packages, this aspect does not
  apply.

* The behavior of package's installed files: packages usually have an
  expected way of having their files used. They may be executed or
  interpreted. If the architecture of the package that installed them
  is exposed in the process of their intended use, their interface is
  considered architecture-dependent.

  For instance, shared and static libraries are inherently
  architecture-dependent. They therefore prohibit the use of "Multi-
  Arch: foreign" unless they are not intended to be used by other
  packages.  Whilst binary executables generally differ across
  architectures, the exposed interface can be independent of the
  architecture used to execute. Architecture exposure can happen via
  the command line arguments, the data exchanged or the way they
  process files. Last but not least, data files can have architecture-
  dependent structure.

* Maintainer scripts and triggers: A package can behave in an
  architecture dependent way, when the behavior of maintainer scripts
  or invoked triggers depends on the architecture. For instance, byte-
  compiling source files into architecture-dependent bytecode during
  "postinst" may turn the interface of a package architecture-
  dependent.

* The dependencies of a package: A package may expose functionality of
  other packages by depending on them and thereby provide an
  architecture-dependent interface itself. The ABI of a shared library
  linked into an executable does not usually contribute to the
  interface, but the behavior of library functions used may do so.
  Development packages for shared libraries necessarily expose their
  own dependencies as their interface since they enable others to link
  such libraries. An extreme example is transitional packages, whose
  main purpose is to expose the functionality of their dependency.
  Therefore, transitional packages should copy the "Architecture" and
  "Multi-Arch" field from their target.

* Implicit and foreign dependencies of a package: Essential packages
  are implicitly depended upon and need not be included in "Depends".
  Yet their behaviour can be architecture-dependent. For instance,
  using "dpkg --print-architecture" can be used to emit the native
  architecture even though "dpkg" is marked "Multi-Arch: foreign".
  Similarly, calling "pkgconf" (without a prefix) will behave
  differently on different architectures as its search path is
  architecture-dependent even though "pkgconf-bin" is considered
  "Multi-Arch: foreign".

The interfaces of a package are determined by its maintainer.
However, some packages might expose architecture-specific dependencies
when other packages use them in a manner not intended by the
maintainer.  This can happen when it is not clear which parts of the
package are its interfaces.

In such cases, where the package satisfies the criterion for "Multi-
Arch: foreign" but might expose architecture dependency, because it is
not clear which parts of the package are its interfaces, the
interfaces of the package should be described in the file
"debian/README.multiarch".

Conversely, packages must not use other packages in ways declined by
their "debian/README.multiarch".


5.6.34.3. "Multi-Arch: same"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This means that other packages with the exact same name and version,
but different architectures, can be installed concurrently.  All those
packages  must be declared "Multi-Arch: same".

For a given file name, if the package for one architecture installs a
file there, then the packages for every other architecture must either
install no file there, or a bit-identical file.  Given this
restriction, such packages usually install most of their files below
"/usr/lib/${DEB_HOST_MULTIARCH}".

The maintainer scripts must be prepared to be configured or
deconfigured multiple times. In particular, "postrm" must not assume
that all instances of the package (e.g., instances for other
architectures) are gone. It may check the
"DPKG_MAINTSCRIPT_PACKAGE_REFCOUNT" environment variable set by
"dpkg".


5.6.34.4. "Multi-Arch: allowed"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This means the same as "Multi-Arch: no" except that a package
depending on this package may choose to treat it as though it were
marked "Multi-Arch: foreign".  This is done by appending ":any" to the
name of the package in the dependency relation field.  For example,
where foo is "Multi-Arch: allowed", bar might have "Depends: foo:any
(>= 1.0)".  Then bar's dependency on foo is satisfied even when bar
and foo have different architectures.

Only a "Multi-Arch: allowed" package satisfies a dependency with the
":any" suffix.

This value should be used rarely. It exists for cases where the
package can be used in an architecture-dependent way or in an
architecture-independent way and the decision of which applies is
deferred to the depender. The most common use is with programming
language interpreters that enable loading architecture-dependent
plugins.

Since removing this value tends to break reverse dependencies that
employ ":any", uses of it should be discussed with *debian-
devel@lists.debian.org* first.


5.6.35. "Build-Profiles"
------------------------

This field occurs in the binary package sections of a source template
control file. It expresses whether the binary package is to be
produced, given a set of enabled build profiles.  The condition uses
the same *restriction formula syntax <s-restrictions>* as the "Build-
Depends" field. In the following example, "libglib2.0-tests" is only
built if both the "noinsttest" and "nogir" build profiles are not
enabled:

   # Build if (!noinsttest) && (!nogir)
   Package: libglib2.0-tests
   Build-Profiles: <!noinsttest !nogir>

If a binary package stanza in a source package template control file
does not contain a "Build-Profiles" field, this means that it builds
unconditionally with respect to build profiles.  If a binary package
stanza in a source package template control file is annotated with a
"Build-Profiles" field, then that binary package is generated if and
only if the condition expressed by field's value evaluates to true.


5.7. User-defined fields
========================

Additional user-defined fields may be added to the source package
template control file. Such fields will be ignored, and not copied to
(for example) binary or Debian source control files or Debian upload
changes control files.

If you wish to add additional unsupported fields to these output files
you should use the mechanism described here.

Fields in the source package template control file with names starting
"X", followed by one or more of the letters "BCS" and a hyphen "-",
will be copied to the output files. Only the part of the field name
after the hyphen will be used in the output file. Where the letter "B"
is used the field will appear in binary package control files, where
the letter "S" is used in Debian source control files and where "C" is
used in Debian upload changes control files.

For example, if the source package template control file contains the
field

   XBS-Comment: I stand between the candle and the star.

then the binary and Debian source control files will contain the field

   Comment: I stand between the candle and the star.


5.8. Obsolete fields
====================

The following fields have been obsoleted and may be found in packages
conforming with previous versions of the Policy.


5.8.1. "DM-Upload-Allowed"
--------------------------

Indicates that Debian Maintainers may upload this package to the
Debian archive. The only valid value is "yes". This field was used to
regulate uploads by Debian Maintainers, See the General Resolution
Endorse the concept of Debian Maintainers for more details.

[1] "dpkg"'s internal databases are in a similar format.

[2] The stanzas somtimes used to be referred to as paragraphs, but
    that caused confusion with text paragraphs in prose, so it is now
    considered a discouraged term.

[3] This folding method is similar to RFC 5322, allowing control files
    that contain only one stanza and no multiline fields to be read by
    parsers written for RFC 5322.

[4] It is customary to leave a space after the package name if a
    version number is specified.

[5] In the past, people specified the full version number in the
    Standards-Version field, for example "2.3.0.0". Since minor patch-
    level changes don't introduce new policy, it was thought it would
    be better to relax policy and only require the first 3 components
    to be specified, in this example "2.3.0". All four components may
    still be used if someone wishes to do so.

[6] Alphanumerics are "A-Za-z0-9" only.

[7] One common use of "~" is for upstream pre-releases. For example,
    "1.0~beta1~svn1245" sorts earlier than "1.0~beta1", which sorts
    earlier than "1.0".

[8] The author of this manual has heard of a package whose versions
    went "1.1", "1.2", "1.3", "1", "2.1", "2.2", "2" and so forth.

[9] Completely empty lines will not be rendered as blank lines.
    Instead, they will cause the parser to think you're starting a
    whole new record in the control file, and will therefore likely
    abort with an error.

[10] Example distribution names in the Debian archive used in
     ".changes" files are:

     *unstable*
        This distribution value refers to the *developmental* part of
        the Debian distribution tree. Most new packages, new upstream
        versions of packages and bug fixes go into the *unstable*
        directory tree.

     *experimental*
        The packages with this distribution value are deemed by their
        maintainers to be high risk. Oftentimes they represent early
        beta or developmental packages from various sources that the
        maintainers want people to try, but are not ready to be a part
        of the other parts of the Debian distribution tree.

     Others are used for updating stable releases or for security
     uploads. More information is available in the Debian Developer's
     Reference, section "The Debian archive".

[11] The source formats currently supported by the Debian archive
     software are "1.0", "3.0 (native)", and "3.0 (quilt)".

[12] Other urgency values are supported with configuration changes in
     the archive software but are not used in Debian. The urgency
     affects how quickly a package will be considered for inclusion
     into the "testing" distribution and gives an indication of the
     importance of any fixes included in the upload. "Emergency" and
     "critical" are treated as synonymous.

[13] A space after each comma is conventional.

[14] That is, the parts which are not the ".dsc".

[15] Annotated tag objects have distinct IDs from the IDs of the
     commits to which they point.  Many Git commands on operating on
     tags dereference the tag immediately, and show you the ID of the
     commit object and not of the tag object, but these are not the
     same.

[16] As an exception, the "libc6" package is marked "Multi-Arch: same"
     despite not fully complying with this requirement, because the
     location of the dynamic loader is not unique across architectures
     and cannot be changed without breakig ABI.



6. Package maintainer scripts and installation procedure
********************************************************


6.1. Introduction to package maintainer scripts
===============================================

It is possible to supply scripts as part of a package which the
package management system will run for you when your package is
installed, upgraded or removed.

These scripts are the package metadata files "preinst", "postinst",
"prerm" and "postrm". They must be proper executable files; if they
are scripts (which is recommended), they must start with the usual
"#!" convention. They should be readable and executable by anyone, and
must not be world-writable.

The package management system looks at the exit status from these
scripts. It is important that they exit with a non-zero status if
there is an error, so that the package management system can stop its
processing. For shell scripts this means that you *almost always* need
to use "set -e" (this is usually true when writing shell scripts, in
fact). It is also important, of course, that they exit with a zero
status if everything went well.

Additionally, packages interacting with users using "debconf" in the
"postinst" script should install a "config" script as a package
metadata file. See Prompting in maintainer scripts for details.

When a package is upgraded a combination of the scripts from the old
and new packages is called during the upgrade procedure. If your
scripts are going to be at all complicated you need to be aware of
this, and may need to check the arguments to your scripts.

Broadly speaking the "preinst" is called before (a particular version
of) a package is unpacked, and the "postinst" afterwards; the "prerm"
before (a version of) a package is removed and the "postrm"
afterwards.

Programs called from maintainer scripts should not normally have a
path prepended to them. Before installation is started, the package
management system checks to see if the programs "ldconfig", "start-
stop-daemon", and "update-rc.d" can be found via the "PATH"
environment variable. Those programs, and any other program that one
would expect to be in the "PATH", should thus be invoked without an
absolute pathname. Maintainer scripts should also not reset the
"PATH", though they might choose to modify it by prepending or
appending package-specific directories. These considerations really
apply to all shell scripts.


6.2. Maintainer scripts idempotency
===================================

It is necessary for the error recovery procedures that the scripts be
idempotent. This means that if it is run successfully, and then it is
called again, it doesn't bomb out or cause any harm, but just ensures
that everything is the way it ought to be. If the first call failed,
or aborted half way through for some reason, the second call should
merely do the things that were left undone the first time, if any, and
exit with a success status if everything is OK.  [1]


6.3. Controlling terminal for maintainer scripts
================================================

Maintainer scripts are not guaranteed to run with a controlling
terminal and may not be able to interact with the user. They must be
able to fall back to noninteractive behavior if no controlling
terminal is available. Maintainer scripts that prompt via a program
conforming to the Debian Configuration Management Specification (see
Prompting in maintainer scripts) may assume that program will handle
falling back to noninteractive behavior.

For high-priority prompts without a reasonable default answer,
maintainer scripts may abort if there is no controlling terminal.
However, this situation should be avoided if at all possible, since it
prevents automated or unattended installs. In most cases, users will
consider this to be a bug in the package.


6.4. Exit status
================

Each script must return a zero exit status for success, or a nonzero
one for failure, since the package management system looks for the
exit status of these scripts and determines what action to take next
based on that datum.


6.5. Summary of ways maintainer scripts are called
==================================================

What follows is a summary of all the ways in which maintainer scripts
may be called along with what facilities those scripts may rely on
being available at that time. Script names preceded by new- are the
scripts from the new version of a package being installed, upgraded
to, or downgraded to. Script names preceded by old- are the scripts
from the old version of a package that is being upgraded from or
downgraded from.

The "preinst" script may be called in the following ways:

   "new-preinst" install
   "new-preinst" install *old-version* *new-version*
   "new-preinst" upgrade *old-version* *new-version*

   The package will not yet be unpacked, so the "preinst" script
   cannot rely on any files included in its package. Only essential
   packages and pre-dependencies ("Pre-Depends") may be assumed to be
   available. Pre-dependencies will have been configured at least
   once, but at the time the "preinst" is called they may only be in
   an "Unpacked" or "Half-Configured" state if a previous version of
   the pre-dependency was completely configured and has not been
   removed since then.

"old-preinst" abort-upgrade *new-version*
   Called during error handling of an upgrade that failed after
   unpacking the new package because the "postrm upgrade" action
   failed. The unpacked files may be partly from the new version or
   partly missing, so the script cannot rely on files included in the
   package. Package dependencies may not be available. Pre-
   dependencies will be at least "Unpacked" following the same rules
   as above, except they may be only "Half-Installed" if an upgrade of
   the pre-dependency failed.  [2]

The "postinst" script may be called in the following ways:

"postinst" configure *most-recently-configured-version*
   The files contained in the package will be unpacked. All package
   dependencies will at least be "Unpacked". If there are no circular
   dependencies involved, all package dependencies will be configured.
   For behavior in the case of circular dependencies, see the
   discussion in Binary Dependencies - Depends, Recommends, Suggests,
   Enhances, Pre-Depends.

   "old-postinst" abort-upgrade *new-version*
   "conflictor's-postinst" abort-remove in-favour *package* *new-version*
   "postinst" abort-remove
   "deconfigured's-postinst" abort-deconfigure in-favour *failed-install-package* *version* [ removing conflicting-package version ]

   The files contained in the package will be unpacked. All package
   dependencies will at least be "Half-Installed" and will have
   previously been configured and not removed. However, dependencies
   may not be configured or even fully unpacked in some error
   situations.  [3] The "postinst" should still attempt any actions
   for which its dependencies are required, since they will normally
   be available, but consider the correct error handling approach if
   those actions fail. Aborting the "postinst" action if commands or
   facilities from the package dependencies are not available is often
   the best approach.

The "prerm" script may be called in the following ways:

   "prerm" remove
   "old-prerm" upgrade *new-version*
   "conflictor's-prerm" remove in-favour package *new-version*
   "deconfigured's-prerm" deconfigure in-favour *package-being-installed* *version* [removing conflicting-package version]

   The package whose "prerm" is being called will be at least "Half-
   Installed". All package dependencies will at least be "Half-
   Installed" and will have previously been configured and not
   removed. If there was no error, all dependencies will at least be
   "Unpacked", but these actions may be called in various error states
   where dependencies are only "Half-Installed" due to a partial
   upgrade.

"new-prerm" failed-upgrade *old-version* *new-version*
   Called during error handling when "prerm upgrade" fails. The new
   package will not yet be unpacked, and all the same constraints as
   for "preinst upgrade" apply.

The "postrm" script may be called in the following ways:

   "postrm" remove
   "postrm" purge
   "old-postrm" upgrade *new-version*
   "disappearer's-postrm" disappear overwriter *overwriter-version*

   The "postrm" script is called after the package's files have been
   removed or replaced. The package whose "postrm" is being called may
   have previously been deconfigured and only be "Unpacked", at which
   point subsequent package changes do not consider its dependencies.
   Therefore, all "postrm" actions must only rely on essential
   packages and must gracefully skip any actions that require the
   package's dependencies if those dependencies are unavailable. [4]

"new-postrm" failed-upgrade *old-version* *new-version*
   Called when the old "postrm upgrade" action fails. The new package
   will be unpacked, but only essential packages and pre-dependencies
   can be relied on. Pre-dependencies will either be configured or
   will be "Unpacked" or "Half-Configured" but previously had been
   configured and was never removed.

   "new-postrm" abort-install
   "new-postrm" abort-install *old-version* *new-version*
   "new-postrm" abort-upgrade *old-version* *new-version*

   Called before unpacking the new package as part of the error
   handling of "preinst" failures. May assume the same state as
   "preinst" can assume.


6.6. Details of unpack phase of installation or upgrade
=======================================================

The procedure on installation/upgrade/overwrite/disappear (i.e., when
running "dpkg --unpack", or the unpack stage of "dpkg --install") is
as follows.  [5] In each case, if a major error occurs (unless listed
below) the actions are, in general, run backwards - this means that
the maintainer scripts are run with different arguments in reverse
order. These are the "error unwind" calls listed below.

1. Notify the currently installed package:

   1. If a version of the package is already "Installed", call

         old-prerm upgrade *new-version*

   2. If the script runs but exits with a non-zero exit status, "dpkg"
      will attempt:

         new-prerm failed-upgrade *old-version* *new-version*

      If this works, the upgrade continues. If this does not work, the
      error unwind:

         *old-postinst* abort-upgrade *new-version*

      If this works, then the *old-version* is "Installed", if not,
      the old version is in a "Half-Configured" state.

2. If a "conflicting" package is being removed at the same time, or if
   any package will be broken (due to "Breaks"):

   1. If "--auto-deconfigure" is specified, call, for each package to
      be deconfigured due to "Breaks":

         *deconfigured's-prerm* deconfigure \
             in-favour *package-being-installed* *version*

      Error unwind:

         *deconfigured's-postinst* abort-deconfigure \
             in-favour *package-being-installed-but-failed* *version*

      The deconfigured packages are marked as requiring configuration,
      so that if "--install" is used they will be configured again if
      possible.

   2. If any packages depended on a conflicting package being removed
      and "--auto-deconfigure" is specified, call, for each such
      package:

         *deconfigured's-prerm* deconfigure \
            in-favour *package-being-installed* *version* \
            removing *conflicting-package* *version*

      Error unwind:

         *deconfigured's-postinst* abort-deconfigure \
             in-favour *package-being-installed-but-failed* *version* \
             removing *conflicting-package* *version*

      The deconfigured packages are marked as requiring configuration,
      so that if "--install" is used they will be configured again if
      possible.

   3. To prepare for removal of each conflicting package, call:

         *conflictor's-prerm* remove \
             in-favour *package* *new-version*

      Error unwind:

         *conflictor's-postinst* abort-remove \
             in-favour *package* *new-version*

3. Run the "preinst" of the new package:

   1. If the package is being upgraded, call:

         *new-preinst* upgrade *old-version* *new-version*

      If this fails, we call:

         *new-postrm* abort-upgrade *old-version* *new-version*

      1. If that works, then

            *old-postinst* abort-upgrade *new-version*

         is called. If this works, then the old version is in an
         "Installed" state, or else it is left in an "Unpacked" state.

      2. If it fails, then the old version is left in an "Half-
         Installed" state.

   2. Otherwise, if the package had some configuration files from a
      previous version installed (i.e., it is in the "Config-Files"
      state):

         *new-preinst* install *old-version* *new-version*

      Error unwind:

         *new-postrm* abort-install *old-version* *new-version*

      If this fails, the package is left in a "Half-Installed" state,
      which requires a reinstall. If it works, the packages is left in
      a "Config-Files" state.

   3. Otherwise (i.e., the package was completely purged):

         *new-preinst* install

      Error unwind:

         *new-postrm* abort-install

      If the error-unwind fails, the package is in a "Half-Installed"
      phase, and requires a reinstall. If the error unwind works, the
      package is in the "Not-Installed" state.

4. The new package's files are unpacked, overwriting any that may be
   on the system already, for example any from the old version of the
   same package or from another package. Backups of the old files are
   kept temporarily, and if anything goes wrong the package management
   system will attempt to put them back as part of the error unwind.

   It is an error for a package to contain files which are on the
   system in another package, unless "Replaces" is used (see
   Overwriting files and replacing packages - Replaces).

   It is a more serious error for a package to contain a plain file or
   other kind of non-directory where another package has a directory
   (again, unless "Replaces" is used). This error can be overridden if
   desired using "--force-overwrite-dir", but this is not advisable.

   Packages which overwrite each other's files produce behavior which,
   though deterministic, is hard for the system administrator to
   understand. It can easily lead to "missing" programs if, for
   example, a package is unpacked which overwrites a file from another
   package, and is then removed again.  [6]

   A directory will never be replaced by a symbolic link to a
   directory or vice versa; instead, the existing state (symlink or
   not) will be left alone and "dpkg" will follow the symlink if there
   is one.

5. If the package is being upgraded:

   1. Call:

         *old-postrm* upgrade *new-version*

   2. If this fails, "dpkg" will attempt:

         *new-postrm* failed-upgrade *old-version* *new-version*

      If this works, installation continues. If not, Error unwind:

         *old-preinst* abort-upgrade *new-version*

      If this fails, the old version is left in a "Half-Installed"
      state. If it works, dpkg now calls:

         *new-postrm* abort-upgrade *old-version* *new-version*

      If this fails, the old version is left in a "Half-Installed"
      state. If it works, dpkg now calls:

         *old-postinst* abort-upgrade *new-version*

      If this fails, the old version is in an "Unpacked" state.

   This is the point of no return. If "dpkg" gets this far, it won't
   back off past this point if an error occurs. This will leave the
   package in a fairly bad state, which will require a successful re-
   installation to clear up, but it's when "dpkg" starts doing things
   that are irreversible.

6. Any files which were in the old version of the package but not in
   the new are removed.

7. The new file list replaces the old.

8. The new maintainer scripts replace the old.

9. Any packages all of whose files have been overwritten during the
   installation, and which aren't required for dependencies, are
   considered to have been removed. For each such package

   1. "dpkg" calls:

         *disappearer's-postrm* disappear \
             *overwriter* *overwriter-version*

   2. The package's maintainer scripts are removed.

   3. It is noted in the status database as being in a sane state,
      namely "Not-Installed" (any conffiles it may have are ignored,
      rather than being removed by "dpkg"). Note that disappearing
      packages do not have their prerm called, because "dpkg" doesn't
      know in advance that the package is going to vanish.

10. Any files in the package we're unpacking that are also listed in
    the file lists of other packages are removed from those lists.
    (This will lobotomize the file list of the "conflicting" package
    if there is one.)

11. The backup files made during installation, above, are deleted.

12. The new package's status is now sane, and recorded as "Unpacked".

    Here is another point of no return: if the conflicting package's
    removal fails we do not unwind the rest of the installation. The
    conflicting package is left in a half-removed limbo.

13. If there was a conflicting package we go and do the removal
    actions (described below), starting with the removal of the
    conflicting package's files (any that are also in the package
    being unpacked have already been removed from the conflicting
    package's file list, and so do not get removed now).


6.7. Details of configuration
=============================

When we configure a package (this happens with "dpkg --install" and
"dpkg --configure"), we first update any "conffile"s and then call:

   *postinst* configure *most-recently-configured-version*

No attempt is made to unwind after errors during configuration. If the
configuration fails, the package is in a "Half-Configured" state, and
an error message is generated.

If there is no most recently configured version "dpkg" will pass a
null argument.  [7]


6.8. Details of removal and/or configuration purging
====================================================

   1. *prerm* remove

   If prerm fails during replacement due to conflict

      *conflictor's-postinst* abort-remove \
          in-favour *package* *new-version*

   Or else we call:

      *postinst* abort-remove

   If this fails, the package is in a "Half-Configured" state, or else
   it remains "Installed".

2. The package's files are removed (except "conffile"s).

   3. *postrm* remove

   If it fails, there's no error unwind, and the package is in an
   "Half-Installed" state.

4. All the maintainer scripts except the "postrm" are removed.

   If we aren't purging the package we stop here. Note that packages
   which have no "postrm" and no "conffile"s are automatically purged
   when removed, as there is no difference except for the "dpkg"
   status.

5. The "conffile"s and any backup files ("~"-files, "#*#" files,
   "%"-files, ".dpkg-{old,new,tmp}", etc.) are removed.

   6. *postrm* purge

   If this fails, the package remains in a "Config-Files" state.

7. The package's file list is removed.

[1] This is so that if an error occurs, the user interrupts "dpkg" or
    some other unforeseen circumstance happens you don't leave the
    user with a badly-broken package when "dpkg" attempts to repeat
    the action.

[2] This can happen if the new version of the package no longer pre-
    depends on a package that had been partially upgraded.

[3] For example, suppose packages foo and bar are "Installed" with foo
    depending on bar. If an upgrade of bar were started and then
    aborted, and then an attempt to remove foo failed because its
    "prerm" script failed, foo's "postinst abort-remove" would be
    called with bar only "Half-Installed".

[4] This is often done by checking whether the command or facility the
    "postrm" intends to call is available before calling it. For
    example:

       if [ "$1" = purge ] && [ -e /usr/share/debconf/confmodule ]; then
           . /usr/share/debconf/confmodule db_purge
       fi

    in "postrm" purges the "debconf" configuration for the package if
    debconf is installed.

[5] See Maintainer script flowcharts for flowcharts illustrating the
    processes described here.

[6] Part of the problem is due to what is arguably a bug in "dpkg".

[7] Historical note: Truly ancient (pre-1997) versions of "dpkg"
    passed "<unknown>" (including the angle brackets) in this case.
    Even older ones did not pass a second argument at all, under any
    circumstance. Note that upgrades using such an old dpkg version
    are unlikely to work for other reasons, even if this old argument
    behavior is handled by your postinst script.



7. Declaring relationships between packages
*******************************************


7.1. Syntax of relationship fields
==================================

These fields all have a uniform syntax. They are a list of package
names separated by commas.

In the "Depends", "Recommends", "Suggests", "Pre-Depends", "Build-
Depends", "Build-Depends-Indep" and "Build-Depends-Arch" control
fields of the package, which declare dependencies on other packages,
the package names listed may also include lists of alternative package
names, separated by vertical bar (pipe) symbols "|". In such a case,
that part of the dependency can be satisfied by any one of the
alternative packages. (Alternative dependencies in "Build-Depends",
"Build-Depends-Indep", and "Build-Depends-Arch" are interpreted
specially by Debian autobuilders. See Relationships between source and
binary packages for more details.)

All of the fields may restrict their applicability to particular
versions of each named package. This is done in parentheses after each
individual package name; the parentheses should contain a relation
from the list below followed by a version number, in the format
described in Version.

The relations allowed are "<<", "<=", "=", ">=" and ">>" for strictly
earlier, earlier or equal, exactly equal, later or equal and strictly
later, respectively.  [1]

Whitespace may appear at any point in the version specification
subject to the rules in Syntax of control files, and must appear where
it's necessary to disambiguate; it is not otherwise significant. All
of the relationship fields can only be folded in source package
template control files. For consistency and in case of future changes
to "dpkg" it is recommended that a single space be used after a
version relationship and before a version number; it is also
conventional to put a single space after each comma, on either side of
each vertical bar, and before each open parenthesis. When opening a
continuation line in a relationship field, it is conventional to do so
after a comma and before the space following that comma.

For example, a list of dependencies might appear as:

   Package: mutt
   Version: 1.3.17-1
   Depends: libc6 (>= 2.2.1), default-mta | mail-transport-agent


7.1.1. Restrictions
-------------------

Relationships may be restricted to a certain set of architectures or
build profiles. This is indicated in brackets after each individual
package name and the optional version specification. There are two
types of restriction.  Architecture restriction lists are enclosed in
a pair of opening and closing square brackets, the specifics of which
are *described below <s-architecture-restrictions>*. Build profile
restriction lists are enclosed by pairs of opening and closing angle
brackets and are also *described in detail below <s-profile-
restrictions>*.

There can be at most one architecture restriction list per dependency
alternative, but there can be more than one build profile restriction
list. One or more build profile restriction lists form a build profile
restriction formula. If both an architecture restriction list and a
build profile restriction formula are to be applied to a dependency
alternative, then the architecture restriction list must come before
the build profile restriction formula in the field value. The non-
empty sets of terms enclosed in either square or angle brackets must
be separated by whitespace.

A term can be prefixed with an optional exclamation mark and must
consist only of lower case letters ("a-z"), digits ("0-9"), plus ("+")
and minus ("-") signs, slashes ("/") and periods (".").

Architecture restriction lists and build profile restriction formulas
are evaluated differently. Both evaluate to booleans, given a host
architecture and a set of enabled build profiles. These results
indicate whether the dependency alternative should be considered or
ignored. For a dependency alternative to be considered, the
architecture restriction list (if any) and the build profile
restriction formula (if any) must both evaluate to true. A dependency
is ignored if none of its alternatives apply.

The sense in which a dependency is ignored depends on the field in
which the restriction appears.  A restriction in one of the build
relationship fields ("Build-Depends"...) that does not match means
that the build-dependency is not required to be satisfied for the
package to be built.  For example, a restriction might specify that
building a package on a certain architecture requires an additional
dependency; such a restriction does not match on other architectures,
meaning the package can be built there without first installing that
additional dependency.

A restriction appearing in a field describing relationships between
binary packages (such as "Depends") must only appear in the source
package template control file "debian/control".  The dependency is
ignored, in the sense that it will not appear in the corresponding
binary package control file, if the restriction does not match.


7.1.1.1. Architecture restrictions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Architecture restriction lists consist of Debian architecture
specification strings.  Exclamation marks may be prepended to each of
the names. (It is not permitted for some names to be prepended with
exclamation marks while others aren't.)

For build relationship fields ("Build-Depends", "Build-Depends-Indep",
"Build-Depends-Arch", "Build-Conflicts", "Build-Conflicts-Indep" and
"Build-Conflicts-Arch"), if the current Debian host architecture is
not in this list and there are no exclamation marks in the list, or it
is in the list with a prepended exclamation mark, the restriction list
evaluates to false.  This means that the package name and the
associated version specification are ignored completely for the
purposes of defining the relationships.

For example:

   Source: glibc
   Build-Depends-Indep: texinfo
   Build-Depends: kernel-headers-2.2.10 [!hurd-i386],
    hurd-dev [hurd-i386], gnumach-dev [hurd-i386]

requires "kernel-headers-2.2.10" on all architectures other than
hurd-i386 and requires "hurd-dev" and "gnumach-dev" only on hurd-i386.
Here is another example showing multiple architectures separated by
spaces:

   Build-Depends:
    libluajit5.1-dev [i386 amd64 kfreebsd-i386 armel armhf powerpc mips],
    liblua5.1-dev [hurd-i386 ia64 kfreebsd-amd64 s390x sparc],

For binary relationship fields and the "Built-Using" field, the
architecture restriction syntax is only supported in the source
package template control file "debian/control". When the corresponding
binary package control file is generated, the relationship will either
be omitted or included without the architecture restriction based on
the architecture of the binary package. This means that architecture
restrictions must not be used in binary relationship fields for
architecture-independent packages ("Architecture: all").

For example:

   Depends: foo [i386], bar [amd64]

becomes "Depends: foo" when the package is built on the "i386"
architecture, "Depends: bar" when the package is built on the "amd64"
architecture, and omitted entirely in binary packages built on all
other architectures.

If the architecture-restricted dependency is part of a set of
alternatives using "|", that alternative is ignored completely on
architectures that do not match the restriction. For example:

   Build-Depends: foo [!i386] | bar [!amd64]

is equivalent to "bar" on the "i386" architecture, to "foo" on the
"amd64" architecture, and to "foo | bar" on all other architectures.

Relationships may also be restricted to a certain set of architectures
using architecture wildcards in the format described in Architecture
wildcards. The syntax for declaring such restrictions is the same as
declaring restrictions using a certain set of architectures without
architecture wildcards. For example:

   Build-Depends: foo [linux-any], bar [any-i386], baz [!linux-any]

is equivalent to "foo" on architectures using the Linux kernel and any
cpu, "bar" on architectures using any kernel and an i386 cpu, and
"baz" on any architecture using a kernel other than Linux.


7.1.1.2. Build profile restriction formulas
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A build profile restriction formula is a sequence of build profile
restriction lists. In contrast, there must not be more than one
architecture restriction list per dependency alternative.  Each list
is enclosed in angle brackets (less than sign and greater than sign).
Each of the space-separated terms of a restriction list is the
possibly-negated name of a build profile. Negation happens by
prefixing the name with an exclamation mark. Unlike architecture
restriction lists, positive and negative terms may be mixed.

A restriction formula may be evaluated as a disjunctive normal form
expression, given a set of *enabled build profiles*. In other words,
each term within a restriction list is AND-ed together while the
restriction lists in a restriction formula are OR-ed together.
Therefore, the order of terms within restriction lists and the order
of restriction lists within a restriction formula do not matter. A
profile name in a term evaluates to "true" if the profile with its
name is enabled for the build and to "false" otherwise. The result may
be negated by prefixing the profile name with an exclamation mark.

In the following example, the package would depend on "foo" when built
for "i386" or 32-bit ARM architectures and if one of the "nocheck" and
"cross" profiles is not enabled by the builder:

   Build-Depends: foo (>= 1.0) [i386 any-arm] <!nocheck> <!cross>, bar

In the following example, the source package would build-depend on
"foo" only if both the "nocheck" profile and the "cross" profile are
enabled at the same time.

   Build-Depends: foo <nocheck cross>

In the next example, the source package would build-depend on "foo" if
"nopython" is disabled and at least one of "nocheck" and "noinsttest"
is disabled.

   Build-Depends: foo <!nopython !nocheck> <!nopython !noinsttest>

The last example can also be rewritten to this alternative form which
is equivalent in meaning:

   Build-Depends: foo <!nopython !nocheck>, foo <!nopython !noinsttest>


7.2. Binary Dependencies - "Depends", "Recommends", "Suggests", "Enhances", "Pre-Depends"
=========================================================================================

Packages can declare in their control file that they have certain
relationships to other packages - for example, that they cannot be
installed at the same time as certain other packages, and/or that they
depend on the presence of others.

This is done using the "Depends", "Pre-Depends", "Recommends",
"Suggests", "Enhances", "Breaks" and "Conflicts" control fields.
"Breaks" is described in Packages which break other packages - Breaks,
and "Conflicts" is described in Conflicting binary packages -
Conflicts. The rest are described below.

These seven fields are used to declare a dependency relationship by
one package on another. Except for "Enhances" and "Breaks", they
appear in the depending (binary) package's control file. ("Enhances"
appears in the recommending package's control file, and "Breaks"
appears in the version of depended-on package which causes the named
package to break).

A "Depends" field takes effect *only* when a package is to be
configured. It does not prevent a package being on the system in an
unconfigured state while its dependencies are unsatisfied, and it is
possible to replace a package whose dependencies are satisfied and
which is properly installed with a different version whose
dependencies are not and cannot be satisfied; when this is done the
depending package will be left unconfigured (since attempts to
configure it will give errors) and will not function properly. If it
is necessary, a "Pre-Depends" field can be used, which has a partial
effect even when a package is being unpacked, as explained in detail
below. (The other three dependency fields, "Recommends", "Suggests"
and "Enhances", are only used by the various front-ends to "dpkg" such
as "apt-get", "aptitude", and "dselect".)

Since "Depends" only places requirements on the order in which
packages are configured, packages in an installation run are usually
all unpacked first and all configured later.  [2]

If there is a circular dependency among packages being installed or
removed, installation or removal order honoring the dependency order
is impossible, requiring the dependency loop be broken at some point
and the dependency requirements violated for at least one package.
Packages involved in circular dependencies may not be able to rely on
their dependencies being configured before they themselves are
configured, depending on which side of the break of the circular
dependency loop they happen to be on. If one of the packages in the
loop has no "postinst" script, then the cycle will be broken at that
package; this ensures that all "postinst" scripts are run with their
dependencies properly configured if this is possible. Otherwise the
breaking point is arbitrary. Packages should therefore avoid circular
dependencies where possible, particularly if they have "postinst"
scripts.

The meaning of the five dependency fields is as follows:

"Depends"
   This declares an absolute dependency. A package will not be
   configured unless all of the packages listed in its "Depends" field
   have been correctly configured (unless there is a circular
   dependency as described above).

   The "Depends" field should be used if the depended-on package is
   required for the depending package to provide a significant amount
   of functionality.

   The "Depends" field should also be used if the "postinst" or
   "prerm" scripts require the depended-on package to be unpacked or
   configured in order to run. In the case of "postinst configure",
   the depended-on packages will be unpacked and configured first. (If
   both packages are involved in a dependency loop, this might not
   work as expected; see the explanation a few paragraphs back.) In
   the case of "prerm" or other "postinst" actions, the package
   dependencies will normally be at least unpacked, but they may be
   only "Half-Installed" if a previous upgrade of the dependency
   failed.

   Finally, the "Depends" field should be used if the depended-on
   package is needed by the "postrm" script to fully clean up after
   the package removal. There is no guarantee that package
   dependencies will be available when "postrm" is run, but the
   depended-on package is more likely to be available if the package
   declares a dependency (particularly in the case of "postrm
   remove"). The "postrm" script must gracefully skip actions that
   require a dependency if that dependency isn't available.

"Recommends"
   This declares a strong, but not absolute, dependency.

   The "Recommends" field should list packages that would be found
   together with this one in all but unusual installations.

"Suggests"
   This is used to declare that one package may be more useful with
   one or more others. Using this field tells the packaging system and
   the user that the listed packages are related to this one and can
   perhaps enhance its usefulness, but that installing this one
   without them is perfectly reasonable.

"Enhances"
   This field is similar to Suggests but works in the opposite
   direction. It is used to declare that a package can enhance the
   functionality of another package.

"Pre-Depends"
   This field is like "Depends", except that it also forces "dpkg" to
   complete installation of the packages named before even starting
   the installation of the package which declares the pre-dependency,
   as follows:

   When a package declaring a pre-dependency is about to be *unpacked*
   the pre-dependency can be satisfied if the depended-on package is
   either fully configured, *or even if* the depended-on package(s)
   are only in the "Unpacked" or the "Half-Configured" state, provided
   that they have been configured correctly at some point in the past
   (and not removed or partially removed since). In this case, both
   the previously-configured and currently "Unpacked" or "Half-
   Configured" versions must satisfy any version clause in the "Pre-
   Depends" field.

   When the package declaring a pre-dependency is about to be
   *configured*, the pre-dependency will be treated as a normal
   "Depends". It will be considered satisfied only if the depended-on
   package has been correctly configured. However, unlike with
   "Depends", "Pre-Depends" does not permit circular dependencies to
   be broken. If a circular dependency is encountered while attempting
   to honor "Pre-Depends", the installation will be aborted.

   "Pre-Depends" are also required if the "preinst" script depends on
   the named package. It is best to avoid this situation if possible.

   "Pre-Depends" should be used sparingly, preferably only by packages
   whose premature upgrade or installation would hamper the ability of
   the system to continue with any upgrade that might be in progress.

   You should not specify a "Pre-Depends" entry for a package before
   this has been discussed on the "debian-devel" mailing list and a
   consensus about doing that has been reached. See Dependencies.

When selecting which level of dependency to use you should consider
how important the depended-on package is to the functionality of the
one declaring the dependency. Some packages are composed of components
of varying degrees of importance. Such a package should list using
"Depends" the package(s) which are required by the more important
components. The other components' requirements may be mentioned as
Suggestions or Recommendations, as appropriate to the components'
relative importance.


7.3. Packages which break other packages - "Breaks"
===================================================

When one binary package declares that it breaks another, "dpkg" will
refuse to allow the package which declares "Breaks" to be unpacked
unless the broken package is deconfigured first, and it will refuse to
allow the broken package to be reconfigured.

A package will not be regarded as causing breakage merely because its
configuration files are still installed; it must be at least "Half-
Installed".

A special exception is made for packages which declare that they break
their own package name or a virtual package which they provide (see
below): this does not count as a real breakage.

Normally a "Breaks" entry will have an "earlier than" version clause;
such a "Breaks" is introduced in the version of an (implicit or
explicit) dependency which violates an assumption or reveals a bug in
earlier versions of the broken package, or which takes over a file
from earlier versions of the package named in "Breaks". This use of
"Breaks" will inform higher-level package management tools that the
broken package must be upgraded before the new one.

If the breaking package also overwrites some files from the older
package, it should use "Replaces" to ensure this goes smoothly. See
Overwriting files and replacing packages - Replaces for a full
discussion of taking over files from other packages, including how to
use "Breaks" in those cases.

Many of the cases where "Breaks" should be used were previously
handled with "Conflicts" because "Breaks" did not yet exist. Many
"Conflicts" fields should now be "Breaks". See Conflicting binary
packages - Conflicts for more information about the differences.


7.4. Conflicting binary packages - "Conflicts"
==============================================

When one binary package declares a conflict with another using a
"Conflicts" field, "dpkg" will refuse to allow them to be unpacked on
the system at the same time. This is a stronger restriction than
"Breaks", which prevents the broken package from being configured
while the breaking package is in the "Unpacked" state but allows both
packages to be unpacked at the same time.

If one package is to be unpacked, the other must be removed first. If
the package being unpacked is marked as replacing (see Overwriting
files and replacing packages - Replaces, but note that "Breaks" should
normally be used in this case) the one on the system, or the one on
the system is marked as deselected, or both packages are marked
"Essential", then "dpkg" will automatically remove the package which
is causing the conflict. Otherwise, it will halt the installation of
the new package with an error. This mechanism is specifically designed
to produce an error when the installed package is "Essential", but the
new package is not.

A package will not cause a conflict merely because its configuration
files are still installed; it must be at least "Half-Installed".

A special exception is made for packages which declare a conflict with
their own package name, or with a virtual package which they provide
(see below): this does not prevent their installation, and allows a
package to conflict with others providing a replacement for it. You
use this feature when you want the package in question to be the only
package providing some feature.

Normally, "Breaks" should be used instead of "Conflicts" since
"Conflicts" imposes a stronger restriction on the ordering of package
installation or upgrade and can make it more difficult for the package
manager to find a correct solution to an upgrade or installation
problem. "Breaks" should be used

* when moving a file from one package to another (see Overwriting
  files and replacing packages - Replaces),

* when splitting a package (a special case of the previous one), or

* when the breaking package exposes a bug in or interacts badly with
  particular versions of the broken package.

"Conflicts" should be used

* when two packages provide the same file and will continue to do so,

* in conjunction with "Provides" when only one package providing a
  given virtual facility can be unpacked at a time (see Virtual
  packages - Provides),

* in other cases where one must prevent simultaneous installation of
  two packages for reasons that are ongoing (not fixed in a later
  version of one of the packages) or that must prevent both packages
  from being unpacked at the same time, not just configured.

Be aware that adding "Conflicts" is normally not the best solution
when two packages provide the same files. Depending on the reason for
that conflict, using alternatives or renaming the files is often a
better approach. See, for example, Binaries.

Neither "Breaks" nor "Conflicts" should be used unless two packages
cannot be installed at the same time or installing them both causes
one of them to be broken or unusable. Having similar functionality or
performing the same tasks as another package is not sufficient reason
to declare "Breaks" or "Conflicts" with that package.

A "Conflicts" entry may have an "earlier than" version clause if the
reason for the conflict is corrected in a later version of one of the
packages. However, normally the presence of an "earlier than" version
clause is a sign that "Breaks" should have been used instead. An
"earlier than" version clause in "Conflicts" prevents "dpkg" from
upgrading or installing the package which declares such a conflict
until the upgrade or removal of the conflicted-with package has been
completed, which is a strong restriction.


7.5. Virtual packages - "Provides"
==================================

As well as the names of actual ("concrete") packages, the package
relationship fields "Depends", "Recommends", "Suggests", "Enhances",
"Pre-Depends", "Breaks", "Conflicts", "Build-Depends", "Build-Depends-
Indep", "Build-Depends-Arch", "Build-Conflicts", "Build-Conflicts-
Indep" and "Build-Conflicts-Arch" may mention "virtual packages".

A *virtual package* is one which appears in the "Provides" control
field of another package. The effect is as if the package(s) which
provide a particular virtual package name had been listed by name
everywhere the virtual package name appears. (See also Virtual
packages)

If there are both concrete and virtual packages of the same name, then
the dependency may be satisfied (or the conflict caused) by either the
concrete package with the name in question or any other concrete
package which provides the virtual package with the name in question.
This is so that, for example, supposing we have

   Package: foo
   Depends: bar

and someone else releases an enhanced version of the "bar" package
they can say:

   Package: bar-plus
   Provides: bar

and the "bar-plus" package will now also satisfy the dependency for
the "foo" package.

A "Provides" field may contain version numbers, but only with the
"exactly equal" ("=") relation. Such a version number will be
considered when considering a dependency on or conflict with the
virtual package name.  For example, given the following packages:

   Package: foo
   Depends: bar (>= 1.0)

   Package: bar
   Version: 0.9

   Package: bar-plus
   Provides: bar (= 1.0)

the "bar-plus" package will satisfy the dependency for the "foo"
package with the virtual package name, as above.  If the "Provides"
field does not specify a version number, it will not satisfy versioned
dependencies or violate versioned "Conflicts" or "Breaks". For
example, given the following packages:

   Package: foo
   Depends: bar (>= 1.0)

   Package: bar
   Version: 0.9

   Package: bar-plus
   Provides: bar (= 1.0)

   Package: bar-clone
   Provides: bar

the "bar-plus" package will satisfy the dependency for the "foo"
package, but the "bar-clone" package will not.

To specify which of a set of real packages should be the default to
satisfy a particular dependency on a virtual package, list the real
package as an alternative before the virtual one.

If the virtual package represents a facility that can only be provided
by one real package at a time, such as the mail-transport-agent
virtual package that requires installation of a binary that would
conflict with all other providers of that virtual package (see Mail
transport, delivery and user agents), all packages providing that
virtual package should also declare a conflict with it using
"Conflicts". This will ensure that at most one provider of that
virtual package is unpacked or installed at a time.


7.6. Overwriting files and replacing packages - "Replaces"
==========================================================

Packages can declare in their control file that they should overwrite
files in certain other packages, or completely replace other packages.
The "Replaces" control field has these two distinct purposes.


7.6.1. Overwriting files in other packages
------------------------------------------

It is usually an error for a package to contain files which are on the
system in another package. However, if the overwriting package
declares that it "Replaces" the one containing the file being
overwritten, then "dpkg" will replace the file from the old package
with that from the new. The file will no longer be listed as "owned"
by the old package and will be taken over by the new package.
Normally, "Breaks" should be used in conjunction with "Replaces".  [3]

For example, if a package foo is split into foo and foo-data starting
at version 1.2-3, foo-data would have the fields

   Replaces: foo (<< 1.2-3)
   Breaks: foo (<< 1.2-3)

in its control file. The new version of the package foo would normally
have the field

   Depends: foo-data (>= 1.2-3)

(or possibly "Recommends" or even "Suggests" if the files moved into
foo-data are not required for normal operation).

If a package is completely replaced in this way, so that "dpkg" does
not know of any files it still contains, it is considered to have
"disappeared". It will be marked as not wanted on the system (selected
for removal) and "Not-Installed". Any "conffile"s details noted for
the package will be ignored, as they will have been taken over by the
overwriting package. The package's "postrm" script will be run with a
special argument to allow the package to do any final cleanup
required. See Summary of ways maintainer scripts are called.  [4]

For this usage of "Replaces", virtual packages (see Virtual packages -
Provides) are not considered when looking at a "Replaces" field. The
packages declared as being replaced must be mentioned by their real
names.

This usage of "Replaces" only takes effect when both packages are at
least partially on the system at once. It is not relevant if the
packages conflict unless the conflict has been overridden.


7.6.2. Replacing whole packages, forcing their removal
------------------------------------------------------

Second, "Replaces" allows the packaging system to resolve which
package should be removed when there is a conflict (see Conflicting
binary packages - Conflicts). This usage only takes effect when the
two packages *do* conflict, so that the two usages of this field do
not interfere with each other.

In this situation, the package declared as being replaced can be a
virtual package, so for example, all mail transport agents (MTAs)
would have the following fields in their control files:

   Provides: mail-transport-agent
   Conflicts: mail-transport-agent
   Replaces: mail-transport-agent

ensuring that only one MTA can be unpacked at any one time. See
Virtual packages - Provides for more information about this example.


7.7. Relationships between source and binary packages - "Build-Depends", "Build-Depends-Indep", "Build-Depends-Arch", "Build-Conflicts", "Build-Conflicts-Indep", "Build-Conflicts-Arch"
========================================================================================================================================================================================

Source packages that require certain binary packages to be installed
or absent at the time of building the package may declare
relationships to those binary packages.

This is done using the "Build-Depends", "Build-Depends-Indep", "Build-
Depends-Arch", "Build-Conflicts", "Build-Conflicts-Indep" and "Build-
Conflicts-Arch" control fields.

Build-dependencies on "build-essential" binary packages can be
omitted. Please see Package relationships for more information.

The dependencies and conflicts they define must be satisfied (as
defined earlier for binary packages) in order to invoke the targets in
"debian/rules", as follows:

"clean"
   Only the "Build-Depends" and "Build-Conflicts" fields must be
   satisfied when this target is invoked.

"build-arch", and "binary-arch"
   The "Build-Depends", "Build-Conflicts", "Build-Depends-Arch", and
   "Build-Conflicts-Arch" fields must be satisfied when these targets
   are invoked.

"build-indep", and "binary-indep"
   The "Build-Depends", "Build-Conflicts", "Build-Depends-Indep", and
   "Build-Conflicts-Indep" fields must be satisfied when these targets
   are invoked.

"build" and "binary"
   The "Build-Depends", "Build-Conflicts", "Build-Depends-Indep",
   "Build-Conflicts-Indep", "Build-Depends-Arch", and "Build-
   Conflicts-Arch" fields must be satisfied when these targets are
   invoked.

Alternative dependencies are allowed in the "Build-Depends", "Build-
Depends-Indep", and "Build-Depends-Arch" fields, but Debian's
autobuilders normally discard the dependencies after the first. This
is done to give alternative dependencies a consistent interpretation
that reduces the risk of inconsistencies between repeated builds. If,
for example, the first-listed dependency would normally be available
but is temporarily not installable, the autobuilder fails rather than
install a subsequent dependency that may significantly change the
behavior of the package.

More specifically, Debian autobuilders perform the following
transformation on alternative dependencies in the "Build-Depends",
"Build-Depends-Indep", and "Build-Depends-Arch" fields:

1. Discard any alternatives that are restricted to architectures that
   do not match the host architecture.

2. Discard any alternatives specifying different package names than
   the now-first alternative. (Alternatives specifying the same
   package name are kept to permit relationships such as "foo (<= x) |
   foo (>= y)".)

For example, an autobuilder for the "amd64" architecture would treat
the following dependency:

   foo-special [armhf] | foo (<= 4) | foo (>= 4.2) | bar

as if it were:

   foo (<= 4) | foo (>= 4.2)

The normal effect is to use only the first alternative that is valid
on the relevant architecture and fail if that alternative is not
installable.

While this rule for build dependencies may limit the usefulness of
alternatives, they can still be used to provide flexibility when
building the package outside of Debian's autobuilders.

The autobuilders for the Debian backports and experimental suites do
not perform this transformation and instead use the same dependency
resolution rules as normal package installations to choose which
alternative dependency to install.


7.8. Additional source packages used to build the binary - "Built-Using"
========================================================================

Some binary packages incorporate parts of other packages when built
but do not have to depend on those packages. Examples include linking
with static libraries or incorporating source code from another
package during the build. In this case, the source packages of those
other packages are part of the complete source (the binary package is
not reproducible without them).

When the license of either the incorporated parts or the incorporating
binary package requires that the full source code of the incorporating
binary package be made available, the "Built-Using" field must list
the corresponding source package for any affected binary package
incorporated during the build, [5] including an "exactly equal" ("=")
version relation on the version that was used to build that version of
the incorporating binary package.  [6]

This causes the Debian archive to retain the versions of the source
packages that were actually incorporated.  In particular, if the
versions of the incorporated parts are updated but the incorporating
binary package is not rebuilt, the older versions of the incorporated
parts will remain in the archive in order to satisfy the license.

A package using the source code from the gcc-4.6-source binary package
built from the gcc-4.6 source package would have this field in its
control file:

   Built-Using: gcc-4.6 (= 4.6.0-11)

A package including binaries from grub2 and loadlin would have this
field in its control file:

   Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)

This field should be used only when there are license or DFSG
requirements to retain the referenced source packages.  It should not
be added solely as a way to locate packages that need to be rebuilt
against newer versions of their build dependencies.

[1] The relations "<" and ">" were previously allowed, but they were
    confusingly defined to mean earlier/later or equal rather than
    strictly earlier/later. "dpkg" still supports them with a warning,
    but they are no longer allowed by Debian Policy.

[2] This approach makes dependency resolution easier. If two packages
    A and B are being upgraded, the installed package A depends on
    exactly the installed package B, and the new package A depends on
    exactly the new package B (a common situation when upgrading
    shared libraries and their corresponding development packages),
    satisfying the dependencies at every stage of the upgrade would be
    impossible. This relaxed restriction means that both new packages
    can be unpacked together and then configured in their dependency
    order.

[3] To see why "Breaks" is normally needed in addition to "Replaces",
    consider the case of a file in the package foo being taken over by
    the package foo-data. "Replaces" will allow foo-data to be
    installed and take over that file. However, without "Breaks",
    nothing requires foo to be upgraded to a newer version that knows
    it does not include that file and instead depends on foo-data.
    Nothing would prevent the new foo-data package from being
    installed and then removed, removing the file that it took over
    from foo. After that operation, the package manager would think
    the system was in a consistent state, but the foo package would be
    missing one of its files.

[4] Replaces is a one way relationship. You have to install the
    replacing package after the replaced package.

[5] "Build-Depends" in the source package is not adequate since it
    (rightfully) does not document the exact version used in the
    build.

[6] The archive software might reject packages that refer to non-
    existent sources.



8. Shared libraries
*******************

Packages containing shared libraries must be constructed with a little
care to make sure that the shared library is always available. This is
especially important for packages whose shared libraries are vitally
important, such as the C library (currently "libc6").

This section deals only with public shared libraries: shared libraries
that are placed in directories searched by the dynamic linker by
default or which are intended to be linked against normally and
possibly used by other, independent packages. Shared libraries that
are internal to a particular package or that are only loaded as
dynamic modules are not covered by this section and are not subject to
its requirements.

A shared library is identified by the "SONAME" attribute stored in its
dynamic section. When a binary is linked against a shared library, the
"SONAME" of the shared library is recorded in the binary's "NEEDED"
section so that the dynamic linker knows that library must be loaded
at runtime. The shared library file's full name (which usually
contains additional version information not needed in the "SONAME") is
therefore normally not referenced directly. Instead, the shared
library is loaded by its "SONAME", which exists on the file system as
a symlink pointing to the full name of the shared library. This
symlink must be provided by the package.  Run-time shared libraries
describes how to do this.  [1]

When linking a binary or another shared library against a shared
library, the "SONAME" for that shared library is not yet known.
Instead, the shared library is found by looking for a file matching
the library name with ".so" appended. This file exists on the file
system as a symlink pointing to the shared library.

Shared libraries are normally split into several binary packages. The
"SONAME" symlink is installed by the runtime shared library package,
and the bare ".so" symlink is installed in the development package
since it's only used when linking binaries or shared libraries.
However, there are some exceptions for unusual shared libraries or for
shared libraries that are also loaded as dynamic modules by other
programs.

This section is primarily concerned with how the separation of shared
libraries into multiple packages should be done and how dependencies
on and between shared library binary packages are managed in Debian.
Libraries should be read in conjunction with this section and contains
additional rules for the files contained in the shared library
packages.

[1] This is a convention of shared library versioning, but not a
    requirement. Some libraries use the "SONAME" as the full library
    file name instead and therefore do not need a symlink. Most,
    however, encode additional information about backwards-compatible
    revisions as a minor version number in the file name. The "SONAME"
    itself only changes when binaries linked with the earlier version
    of the shared library may no longer work, but the filename may
    change with each release of the library. See Run-time shared
    libraries for more information.


8.1. Run-time shared libraries
==============================

The run-time shared library must be placed in a package whose name
changes whenever the "SONAME" of the shared library changes. This
allows several versions of the shared library to be installed at the
same time, allowing installation of the new version of the shared
library without immediately breaking binaries that depend on the old
version. [2]

Normally, the run-time shared library and its "SONAME" symlink should
be placed in a package named libraryname*soversion*, where *soversion*
is the version number in the "SONAME" of the shared library.
Alternatively, if it would be confusing to directly append *soversion*
to libraryname (if, for example, libraryname itself ends in a number),
you should use libraryname-*soversion* instead. [3]

To determine the *soversion*, look at the "SONAME" of the library,
stored in the ELF "SONAME" attribute. It is usually of the form
"name.so.major-version" (for example, "libz.so.1"). The version part
is the part which comes after ".so.", so in that example it is "1".
The soname may instead be of the form "name-major-version.so", such as
"libdb-5.1.so", in which case the name would be "libdb" and the
version would be "5.1".

If you have several shared libraries built from the same source tree,
you may lump them all together into a single shared library package
provided that all of their "SONAME"s will always change together. Be
aware that this is not normally the case, and if the "SONAME"s do not
change together, upgrading such a merged shared library package will
be unnecessarily difficult because of file conflicts with the old
version of the package. When in doubt, always split shared library
packages so that each binary package installs a single shared library.

Every time the shared library ABI changes in a way that could break
binaries linked against older versions of the shared library, the
"SONAME" of the library and the corresponding name for the binary
package containing the runtime shared library should change. Normally,
this means the "SONAME" should change any time an interface is removed
from the shared library or the signature of an interface (the number
of parameters or the types of parameters that it takes, for example)
is changed. This practice is vital to allowing clean upgrades from
older versions of the package and clean transitions between the old
ABI and new ABI without having to upgrade every affected package
simultaneously.

The "SONAME" and binary package name need not, and indeed normally
should not, change if new interfaces are added but none are removed or
changed, since this will not break binaries linked against the old
shared library. Correct versioning of dependencies on the newer shared
library by binaries that use the new interfaces is handled via the
"symbols" or "shlibs" system (see Dependencies between the library and
other packages).

The package should install the shared libraries under their normal
names. For example, the libgdbm3 package should install
"libgdbm.so.3.0.0" as "/usr/lib/libgdbm.so.3.0.0". The files should
not be renamed or re-linked by any "prerm" or "postrm" scripts; "dpkg"
will take care of renaming things safely without affecting running
programs, and attempts to interfere with this are likely to lead to
problems.

Shared libraries should not be installed executable, since the dynamic
linker does not require this and trying to execute a shared library
usually results in a core dump.

The run-time library package should include the symbolic link for the
"SONAME" that "ldconfig" would create for the shared libraries. For
example, the libgdbm3 package should include a symbolic link from
"/usr/lib/libgdbm.so.3" to "libgdbm.so.3.0.0". This is needed so that
the dynamic linker (for example "ld.so" or "ld-linux.so.*") can find
the library between the time that "dpkg" installs it and the time that
"ldconfig" is run in the "postinst" script.  [4]

[2] There are some exceptional situations in which co-installation of
    two versions of a shared library is not safe, and the new shared
    library package has to conflict with the previous shared library
    package. This is never desirable, since it causes significant
    disruption during upgrades and potentially breaks unpackaged
    third-party binaries, but is sometimes unavoidable. These
    situations are sufficiently rare that they usually warrant
    project-wide discussion, and are complex enough that the rules for
    them cannot be codified in Debian Policy.

[3] The following command, when run on a shared library, will output
    the name to be used for the Debian package containing that shared
    library:

       objdump -p /path/to/libfoo-bar.so.1.2.3 \
           | sed -n -e's/^[[:space:]]*SONAME[[:space:]]*//p' \
           | LC_ALL=C sed -r -e's/([0-9])\.so\./\1-/; s/\.so(\.|$)//; y/_/-/; s/(.*)/\L&/'

[4] The package management system requires the library to be placed
    before the symbolic link pointing to it in the ".deb" file. This
    is so that when "dpkg" comes to install the symlink (overwriting
    the previous symlink pointing at an older version of the library),
    the new shared library is already in place. In the past, this was
    achieved by creating the library in the temporary packaging
    directory before creating the symlink. Unfortunately, this was not
    always effective, since the building of the tar file in the ".deb"
    depended on the behavior of the underlying file system. Some file
    systems (such as reiserfs) reorder the files so that the order of
    creation is forgotten. Since version 1.7.0, "dpkg" reorders the
    files itself as necessary when building a package. Thus it is no
    longer important to concern oneself with the order of file
    creation.


8.1.1. "ldconfig"
-----------------

Any package installing shared libraries in one of the default library
directories of the dynamic linker (which are currently "/usr/lib" and
"/lib") or a directory that is listed in "/etc/ld.so.conf" [5] must
use "ldconfig" to update the shared library system.

Any such package must have the line "activate-noawait ldconfig" in its
"triggers" control file (i.e. "DEBIAN/triggers").

[5] These are currently "/usr/local/lib" plus directories under "/lib"
    and "/usr/lib" matching the multiarch triplet for the system
    architecture.


8.2. Shared library support files
=================================

If your package contains files whose names do not change with each
change in the library shared object version, you must not put them in
the shared library package. Otherwise, several versions of the shared
library cannot be installed at the same time without filename clashes,
making upgrades and transitions unnecessarily difficult.

It is recommended that supporting files and run-time support programs
that do not need to be invoked manually by users, but are nevertheless
required for the package to function, be placed (if they are binary)
in a subdirectory of "/usr/lib", preferably under "/usr/lib/"package-
name. If the program or file is architecture independent, the
recommendation is for it to be placed in a subdirectory of
"/usr/share" instead, preferably under "/usr/share/"package-name.
Following the package-name naming convention ensures that the file
names change when the shared object version changes.

Run-time support programs that use the shared library but are not
required for the library to function or files used by the shared
library that can be used by any version of the shared library package
should instead be put in a separate package. This package might
typically be named libraryname-tools; note the absence of the
soversion in the package name.

Files and support programs only useful when compiling software against
the library should be included in the development package for the
library.  [6]

[6] For example, a "package-name-config" script or pkg-config
    configuration files.


8.3. Static libraries
=====================

The static library ("libraryname.a") is usually provided in addition
to the shared version. It is placed into the development package (see
below).

In some cases, it is acceptable for a library to be available in
static form only; these cases include:

* libraries for languages whose shared library support is immature or
  unstable

* libraries whose interfaces are in flux or under development
  (commonly the case when the library's major version number is zero,
  or where the ABI breaks across patchlevels)

* libraries which are explicitly intended to be available only in
  static form by their upstream author(s)


8.4. Development files
======================

If there are development files associated with a shared library, the
source package needs to generate a binary development package named
libraryname-dev, or if you need to support multiple development
versions at a time, librarynameapiversion-dev. Installing the
development package must result in installation of all the development
files necessary for compiling programs against that shared library.
[7]

[7] This wording allows the development files to be split into several
    packages, such as a separate architecture-independent libraryname-
    headers, provided that the development package depends on all the
    required additional packages.

In case several development versions of a library exist, you may need
to use "dpkg"'s Conflicts mechanism (see Conflicting binary packages -
Conflicts) to ensure that the user only installs one development
version at a time (as different development versions are likely to
have the same header files in them, which would cause a filename clash
if both were unpacked).

The development package should contain either a symlink or a linker
script [8] for the associated shared library without a version number.
For example, the "libgdbm-dev" package should include a symlink from
"/usr/lib/libgdbm.so" to "libgdbm.so.3.0.0", or a linker script that
achieves the same effect.  This symlink or linker script is needed by
the linker (**ld**) when compiling packages, as it will only look for
"libgdbm.so" when compiling dynamically.

[8] Linker scripts are used when more flexible linking strategies are
    required, such as conditionally linking with an additional library
    or falling back to a static library for some symbols.

If the package installs a linker script, be aware that **ldconfig**
requires the linker script to be shorter than 32 bytes, or contain
either the "GROUP" directive or the string "GNU ld script" in a
comment in the first 512 bytes.

If the package provides Ada Library Information ("*.ali") files for
use with GNAT, these files must be installed read-only (mode 0444) so
that GNAT will not attempt to recompile them. This overrides the
normal file mode requirements given in Permissions and owners.


8.5. Dependencies between the packages of the same library
==========================================================

Typically the development version should have an exact version
dependency on the runtime library, to make sure that compilation and
linking happens correctly. The "${binary:Version}" substitution
variable can be useful for this purpose.  [9]

[9] Previously, "${Source-Version}" was used, but its name was
    confusing and it has been deprecated since dpkg 1.13.19.


8.6. Dependencies between the library and other packages
========================================================

If a package contains a binary or library which links to a shared
library, we must ensure that, when the package is installed on the
system, all of the libraries needed are also installed. These
dependencies must be added to the binary package when it is built,
since they may change based on which version of a shared library the
binary or library was linked with even if there are no changes to the
source of the binary (for example, symbol versions change, macros
become functions or vice versa, or the binary package may determine at
compile-time whether new library interfaces are available and can be
called). To allow these dependencies to be constructed, shared
libraries must provide either a "symbols" file or a "shlibs" file.
These provide information on the package dependencies required to
ensure the presence of interfaces provided by this library. Any
package with binaries or libraries linking to a shared library must
use these files to determine the required dependencies when it is
built. Other packages which use a shared library (for example using
"dlopen()") should compute appropriate dependencies using these files
at build time as well.

The two mechanisms differ in the degree of detail that they provide. A
"symbols" file documents, for each symbol exported by a library, the
minimal version of the package any binary using this symbol will need.
This is typically the version of the package in which the symbol was
introduced. This information permits detailed analysis of the symbols
used by a particular package and construction of an accurate
dependency, but it requires the package maintainer to track more
information about the shared library.

A "shlibs" file, in contrast, only documents the last time the library
ABI changed in any way. It only provides information about the library
as a whole, not individual symbols. When a package is built using a
shared library with only a "shlibs" file, the generated dependency
will require a version of the shared library equal to or newer than
the version of the last ABI change. This generates unnecessarily
restrictive dependencies compared to "symbols" files if none of the
symbols used by the package have changed. This, in turn, could make
upgrades needlessly complex and unnecessarily restrict use of the
package on systems with older versions of the shared libraries.

"shlibs" files also only support a limited range of library SONAMEs,
making it difficult to use "shlibs" files in some unusual corner
cases.  [10]

"symbols" files are therefore recommended for most shared library
packages since they provide more accurate dependencies. For most C
libraries, the additional detail required by "symbols" files is not
too difficult to maintain. However, maintaining exhaustive symbols
information for a C++ library can be quite onerous, so "shlibs" files
may be more appropriate for most C++ libraries. Libraries with a
corresponding udeb must also provide a "shlibs" file, since the udeb
infrastructure does not use "symbols" files.

[10] A "shlibs" file represents an SONAME as a library name and
     version number, such as "libfoo VERSION", instead of recording
     the actual SONAME. If the SONAME doesn't match one of the two
     expected formats ("libfoo-VERSION.so" or "libfoo.so.VERSION"), it
     cannot be represented.


8.6.1. Generating dependencies on shared libraries
--------------------------------------------------

When a package that contains any shared libraries or compiled binaries
is built, it must run "dpkg-shlibdeps" on each shared library and
compiled binary to determine the libraries used and hence the
dependencies needed by the package. [11] To do this, put a call to
"dpkg-shlibdeps" into your "debian/rules" file in the source package.
List all of the compiled binaries, libraries, or loadable modules in
your package. [12] "dpkg-shlibdeps" will use the "symbols" or "shlibs"
files installed by the shared libraries to generate dependency
information. The package must then provide a substitution variable
into which the discovered dependency information can be placed.

If you are creating a udeb for use in the Debian Installer, you will
need to specify that "dpkg-shlibdeps" should use the dependency line
of type "udeb" by adding the "-tudeb" option.  [13] If there is no
dependency line of type "udeb" in the "shlibs" file, "dpkg-shlibdeps"
will fall back to the regular dependency line.

"dpkg-shlibdeps" puts the dependency information into the
"debian/substvars" file by default, which is then used by "dpkg-
gencontrol". You will need to place a "${shlibs:Depends}" variable in
the "Depends" field in the control file of every binary package built
by this source package that contains compiled binaries, libraries, or
loadable modules. If you have multiple binary packages, you will need
to call "dpkg-shlibdeps" on each one which contains compiled libraries
or binaries. For example, you could use the "-T" option to the "dpkg"
utilities to specify a different "substvars" file for each binary
package.  [14]

For more details on "dpkg-shlibdeps", see its manual page.

We say that a binary "foo" *directly* uses a library "libbar" if it is
explicitly linked with that library (that is, the library is listed in
the ELF "NEEDED" attribute, caused by adding "-lbar" to the link line
when the binary is created). Other libraries that are needed by
"libbar" are linked *indirectly* to "foo", and the dynamic linker will
load them automatically when it loads "libbar". A package should
depend on the libraries it directly uses, but not the libraries it
only uses indirectly. The dependencies for the libraries used directly
will automatically pull in the indirectly-used libraries. "dpkg-
shlibdeps" will handle this logic automatically, but package
maintainers need to be aware of this distinction between directly and
indirectly using a library if they have to override its results for
some reason.  [15]

[11] "dpkg-shlibdeps" will use a program like "objdump" or "readelf"
     to find the libraries and the symbols in those libraries directly
     needed by the binaries or shared libraries in the package.

[12] The easiest way to call "dpkg-shlibdeps" correctly is to use a
     package helper framework such as debhelper. If you are using
     debhelper, the "dh_shlibdeps" program will do this work for you.
     It will also correctly handle multi-binary packages.

[13] "dh_shlibdeps" from the "debhelper" suite will automatically add
     this option if it knows it is processing a udeb.

[14] Again, "dh_shlibdeps" and "dh_gencontrol" will handle everything
     except the addition of the variable to the control file for you
     if you're using debhelper, including generating separate
     "substvars" files for each binary package and calling "dpkg-
     gencontrol" with the appropriate flags.

[15] A good example of where this helps is the following: We could
     update "libimlib" with a new version that supports a new revision
     of a graphics format called dgf (but retaining the same major
     version number) and depends on a new library package libdgf4
     instead of the older libdgf3. If we used "ldd" to add
     dependencies for every library directly or indirectly linked with
     a binary, every package that uses "libimlib" would need to be
     recompiled so it would also depend on libdgf4 in order to retire
     the older libdgf3 package. Since dependencies are only added
     based on ELF "NEEDED" attribute, packages using "libimlib" can
     rely on "libimlib" itself having the dependency on an appropriate
     version of "libdgf" and do not need rebuilding.


8.6.2. Shared library ABI changes
---------------------------------

Maintaining a shared library package using either "symbols" or
"shlibs" files requires being aware of the exposed ABI of the shared
library and any changes to it. Both "symbols" and "shlibs" files
record every change to the ABI of the shared library; "symbols" files
do so per public symbol, whereas "shlibs" files record only the last
change for the entire library.

There are two types of ABI changes: ones that are backward-compatible
and ones that are not. An ABI change is backward-compatible if any
reasonable program or library that was linked with the previous
version of the shared library will still work correctly with the new
version of the shared library.  [16] Adding new symbols to the shared
library is a backward-compatible change. Removing symbols from the
shared library is not. Changing the behavior of a symbol may or may
not be backward-compatible depending on the change; for example,
changing a function to accept a new enum constant not previously used
by the library is generally backward-compatible, but changing the
members of a struct that is passed into library functions is generally
not unless the library takes special precautions to accept old
versions of the data structure.

ABI changes that are not backward-compatible normally require changing
the "SONAME" of the library and therefore the shared library package
name, which forces rebuilding all packages using that shared library
to update their dependencies and allow them to use the new version of
the shared library. For more information, see Run-time shared
libraries. The remainder of this section will deal with backward-
compatible changes.

Backward-compatible changes require either updating or recording the
minimal-version for that symbol in "symbols" files or updating the
version in the dependencies in "shlibs" files. For more information on
how to do this in the two formats, see The symbols File Format and The
shlibs File Format. Below are general rules that apply to both files.

The easy case is when a public symbol is added. Simply add the version
at which the symbol was introduced (for "symbols" files) or update the
dependency version (for "shlibs") files. But special care should be
taken to update dependency versions when the behavior of a public
symbol changes. This is easy to neglect, since there is no automated
method of determining such changes, but failing to update versions in
this case could result in binary packages with too-weak dependencies
that will fail at runtime, possibly in ways that can cause security
vulnerabilities. If the package maintainer believes that a symbol
behavior change could have occurred but isn't sure, it's safer to
update the version rather than leave it unmodified. This may result in
unnecessarily strict dependencies, but it ensures that packages whose
dependencies are satisfied will work properly.

A common example of when a change to the dependency version is
required is a function that takes an enum or struct argument that
controls what the function does. For example:

   enum library_op { OP_FOO, OP_BAR };
   int library_do_operation(enum library_op);

If a new operation, "OP_BAZ", is added, the minimal-version of
"library_do_operation" (for "symbols" files) or the version in the
dependency for the shared library (for "shlibs" files) must be
increased to the version at which "OP_BAZ" was introduced. Otherwise,
a binary built against the new version of the library (having detected
at compile-time that the library supports "OP_BAZ") may be installed
with a shared library that doesn't support "OP_BAZ" and will fail at
runtime when it tries to pass "OP_BAZ" into this function.

Dependency versions in either "symbols" or "shlibs" files normally
should not contain the Debian revision of the package, since the
library behavior is normally fixed for a particular upstream version
and any Debian packaging of that upstream version will have the same
behavior. In the rare case that the library behavior was changed in a
particular Debian revision, appending "~" to the end of the version
that includes the Debian revision is recommended, since this allows
backports of the shared library package using the normal backport
versioning convention to satisfy the dependency.

[16] An example of an "unreasonable" program is one that uses library
     interfaces that are documented as internal and unsupported. If
     the only programs or libraries affected by a change are
     "unreasonable" ones, other techniques, such as declaring "Breaks"
     relationships with affected packages or treating their usage of
     the library as bugs in those packages, may be appropriate instead
     of changing the SONAME.  However, the default approach is to
     change the SONAME for any change to the ABI that could break a
     program.


8.6.3. The "symbols" system
---------------------------

In the following sections, we will first describe where the various
"symbols" files are to be found, then the "symbols" file format, and
finally how to create "symbols" files if your package contains a
shared library.


8.6.3.1. The "symbols" files present on the system
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

"symbols" files for a shared library are normally provided by the
shared library package as a control file, but there are several
override paths that are checked first in case that information is
wrong or missing. The following list gives them in the order in which
they are read by "dpkg-shlibdeps". The first one that contains the
required information is used.

"debian/*/DEBIAN/symbols"
   During the package build, if the package itself contains shared
   libraries with "symbols" files, they will be generated in these
   staging directories by "dpkg-gensymbols" (see Providing a symbols
   file). "symbols" files found in the build tree take precedence over
   "symbols" files from other binary packages.

   These files must exist before "dpkg-shlibdeps" is run or the
   dependencies of binaries and libraries from a source package on
   other libraries from that same source package will not be correct.
   In practice, this means that "dpkg-gensymbols" must be run before
   "dpkg-shlibdeps" during the package build.  [17]

"/etc/dpkg/symbols/package.symbols.arch" and
"/etc/dpkg/symbols/package.symbols"
   Per-system overrides of shared library dependencies. These files
   normally do not exist. They are maintained by the local system
   administrator and must not be created by any Debian package.

"symbols" control files for packages installed on the system
   The "symbols" control files for all the packages currently
   installed on the system are searched last. This will be the most
   common source of shared library dependency information. These files
   can be read with "dpkg-query --control-show package symbols".

Be aware that if a "debian/shlibs.local" exists in the source package,
it will override any "symbols" files. This is the only case where a
"shlibs" is used despite "symbols" files being present. See The shlibs
files present on the system and The shlibs system for more
information.

[17] An example may clarify. Suppose the source package "foo"
     generates two binary packages, "libfoo2" and "foo-runtime". When
     building the binary packages, the contents of the packages are
     staged in the directories "debian/libfoo2" and "debian/foo-
     runtime" respectively. ("debian/tmp" could be used instead of one
     of these.)  Since "libfoo2" provides the "libfoo" shared library,
     it will contain a "symbols" file, which will be installed in
     "debian/libfoo2/DEBIAN/symbols", eventually to be included as a
     control file in that package. When "dpkg-shlibdeps" is run on the
     executable "debian/foo-runtime/usr/bin/foo-prog", it will examine
     the "debian/libfoo2/DEBIAN/symbols" file to determine whether
     "foo-prog"'s library dependencies are satisfied by any of the
     libraries provided by "libfoo2". Since those binaries were linked
     against the just-built shared library as part of the build
     process, the "symbols" file for the newly-built "libfoo2" must
     take precedence over a "symbols" file for any other "libfoo2"
     package already installed on the system.


8.6.3.2. The "symbols" File Format
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following documents the format of the "symbols" control file as
included in binary packages. These files are built from template
"symbols" files in the source package by "dpkg-gensymbols". The
template files support a richer syntax that allows "dpkg-gensymbols"
to do some of the tedious work involved in maintaining "symbols"
files, such as handling C++ symbols or optional symbols that may not
exist on particular architectures. When writing "symbols" files for a
shared library package, refer to *dpkg-gensymbols(1)* for the richer
syntax.

A "symbols" may contain one or more entries, one for each shared
library contained in the package corresponding to that "symbols". Each
entry has the following format:

   library-soname main-dependency-template
    [| alternative-dependency-template]
    [...]
    [* field-name: field-value]
    [...]
    symbol minimal-version[ id-of-dependency-template]

To explain this format, we'll use the "zlib1g" package as an example,
which (at the time of writing) installs the shared library
"/usr/lib/libz.so.1.2.3.4". Mandatory lines will be described first,
followed by optional lines.

"library-soname" must contain exactly the value of the ELF "SONAME"
attribute of the shared library. In our example, this is "libz.so.1".
[18]

"main-dependency-template" has the same syntax as a dependency field
in a binary package control file, except that the string "#MINVER#" is
replaced by a version restriction like "(>= version)" or by nothing if
an unversioned dependency is deemed sufficient. The version
restriction will be based on which symbols from the shared library are
referenced and the version at which they were introduced (see below).
In nearly all cases, "main-dependency-template" will be "package
#MINVER#", where package is the name of the binary package containing
the shared library. This adds a simple, possibly-versioned dependency
on the shared library package. In some rare cases, such as when
multiple packages provide the same shared library ABI, the dependency
template may need to be more complex.

In our example, the first line of the "zlib1g" "symbols" file would
be:

   libz.so.1 zlib1g #MINVER#

Each public symbol exported by the shared library must have a
corresponding symbol line, indented by one space. symbol is the
exported symbol (which, for C++, means the mangled symbol) followed by
"@" and the symbol version, or the string "Base" if there is no symbol
version. "minimal-version" is the most recent version of the shared
library that changed the behavior of that symbol, whether by adding
it, changing its function signature (the parameters, their types, or
the return type), or changing its behavior in a way that is visible to
a caller. "id-of-dependency-template" is an optional field that
references an "alternative-dependency-template"; see below for a full
description.

For example, "libz.so.1" contains the symbols "compress" and
"compressBound". "compress" has no symbol version and last changed its
behavior in upstream version "1:1.1.4". "compressBound" has the symbol
version "ZLIB_1.2.0", was introduced in upstream version "1:1.2.0",
and has not changed its behavior. Its "symbols" file therefore
contains the lines:

   compress@Base 1:1.1.4
   compressBound@ZLIB_1.2.0 1:1.2.0

Packages using only "compress" would then get a dependency on "zlib1g
(>= 1:1.1.4)", but packages using "compressBound" would get a
dependency on "zlib1g (>= 1:1.2.0)".

One or more "alternative-dependency-template" lines may be provided.
These are used in cases where some symbols in the shared library
should use one dependency template while others should use a different
template.  The alternative dependency templates are used only if a
symbol line contains the "id-of-dependency-template" field. The first
alternative dependency template is numbered 1, the second 2, and so
forth.  [19]

Finally, the entry for the library may contain one or more metadata
fields. Currently, the only supported field-name is "Build-Depends-
Package", whose value lists the library development package on which
packages using this shared library declare a build dependency. If this
field is present, "dpkg-shlibdeps" uses it to ensure that the
resulting binary package dependency on the shared library is at least
as strict as the source package dependency on the shared library
development package.  [20] For our example, the "zlib1g" "symbols"
file would contain:

   * Build-Depends-Package: zlib1g-dev

Also see *deb-symbols(5)*.

[18] This can be determined by using the command

        readelf -d /usr/lib/libz.so.1.2.3.4 | grep SONAME

[19] An example of where this may be needed is with a library that
     implements the libGL interface. All GL implementations provide
     the same set of base interfaces, and then may provide some
     additional interfaces only used by programs that require that
     specific GL implementation. So, for example, libgl1-mesa-glx may
     use the following "symbols" file:

        libGL.so.1 libgl1
         | libgl1-mesa-glx #MINVER#
         publicGlSymbol@Base 6.3-1 [...]
         implementationSpecificSymbol@Base 6.5.2-7 1
         [...]

     Binaries or shared libraries using only "publicGlSymbol" would
     depend only on "libgl1" (which may be provided by multiple
     packages), but ones using "implementationSpecificSymbol" would
     get a dependency on "libgl1-mesa-glx (>= 6.5.2-7)".

[20] This field should normally not be necessary, since if the
     behavior of any symbol has changed, the corresponding symbol
     minimal-version should have been increased. But including it
     makes the "symbols" system more robust by tightening the
     dependency in cases where the package using the shared library
     specifically requires at least a particular version of the shared
     library development package for some reason.


8.6.3.3. Providing a "symbols" file
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If your package provides a shared library, you should arrange to
include a "symbols" control file following the format described above
in that package. You must include either a "symbols" control file or a
"shlibs" control file.

Normally, this is done by creating a "symbols" in the source package
named "debian/package.symbols" or "debian/symbols", possibly with
".arch" appended if the symbols information varies by architecture.
This file may use the extended syntax documented in *dpkg-
gensymbols(1)*.  Then, call "dpkg-gensymbols" as part of the package
build process. It will create "symbols" files in the package staging
area based on the binaries and libraries in the package staging area
and the "symbols" files in the source package. [21]

Packages that provide "symbols" files must keep them up-to-date to
ensure correct dependencies in packages that use the shared libraries.
This means updating the "symbols" file whenever a new public symbol is
added, changing the minimal-version field whenever a symbol changes
behavior or signature in a backward-compatible way (see Shared library
ABI changes), and changing the library-soname and main-dependency-
template, and probably all of the minimal-version fields, when the
library changes "SONAME". Removing a public symbol from the "symbols"
file because it's no longer provided by the library normally requires
changing the "SONAME" of the library.  See Run-time shared libraries
for more information on "SONAME"s.

[21] If you are using "debhelper", "dh_makeshlibs" will take care of
     calling either "dpkg-gensymbols" or generating a "shlibs" file as
     appropriate.


8.6.4. The "shlibs" system
--------------------------

The "shlibs" system is a simpler alternative to the "symbols" system
for declaring dependencies for shared libraries. It may be more
appropriate for C++ libraries and other cases where tracking
individual symbols is too difficult. It predated the "symbols" system
and is therefore frequently seen in older packages. It is also
required for udebs, which do not support "symbols".

In the following sections, we will first describe where the various
"shlibs" files are to be found, then how to use "dpkg-shlibdeps", and
finally the "shlibs" file format and how to create them.


8.6.4.1. The "shlibs" files present on the system
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

There are several places where "shlibs" files are found. The following
list gives them in the order in which they are read by "dpkg-
shlibdeps". (The first one which gives the required information is
used.)

"debian/shlibs.local"
   This lists overrides for this package. This file should normally
   not be used, but may be needed temporarily in unusual situations to
   work around bugs in other packages, or in unusual cases where the
   normally declared dependency information in the installed "shlibs"
   file for a library cannot be used. This file overrides information
   obtained from any other source.

"/etc/dpkg/shlibs.override"
   This lists global overrides. This list is normally empty. It is
   maintained by the local system administrator.

"DEBIAN/shlibs" files in the "build directory"
   These files are generated as part of the package build process and
   staged for inclusion as control files in the binary packages being
   built. They provide details of any shared libraries included in the
   same package.

"shlibs" control files for packages installed on the system
   The "shlibs" control files for all the packages currently installed
   on the system. These files can be read using "dpkg-query --control-
   show package shlibs".

"/etc/dpkg/shlibs.default"
   This file lists any shared libraries whose packages have failed to
   provide correct "shlibs" files. It was used when the "shlibs" setup
   was first introduced, but it is now normally empty. It is
   maintained by the "dpkg" maintainer.

If a "symbols" file for a shared library package is available, "dpkg-
shlibdeps" will always use it in preference to a "shlibs", with the
exception of "debian/shlibs.local". The latter overrides any other
"shlibs" or "symbols" files.


8.6.4.2. The "shlibs" File Format
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Each "shlibs" file has the same format. Lines beginning with "#" are
considered to be comments and are ignored. Each line is of the form:

   [type: ]library-name soname-version dependencies ...

We will explain this by reference to the example of the "zlib1g"
package, which (at the time of writing) installs the shared library
"/usr/lib/libz.so.1.2.3.4".

"type" is an optional element that indicates the type of package for
which the line is valid. The only type currently in use is "udeb". The
colon and space after the type are required.

"library-name" is the name of the shared library, in this case "libz".
(This must match the name part of the soname, see below.)

"soname-version" is the version part of the ELF "SONAME" attribute of
the library, determined the same way that the soversion component of
the recommended shared library package name is determined. See Run-
time shared libraries for the details.

"dependencies" has the same syntax as a dependency field in a binary
package control file. It should give details of which packages are
required to satisfy a binary built against the version of the library
contained in the package. See Syntax of relationship fields for
details on the syntax, and Shared library ABI changes for details on
how to maintain the dependency version constraint.

In our example, if the last change to the "zlib1g" package that could
change behavior for a client of that library was in version
"1:1.2.3.3.dfsg-1", then the "shlibs" entry for this library could
say:

   libz 1 zlib1g (>= 1:1.2.3.3.dfsg)

This version restriction must be new enough that any binary built
against the current version of the library will work with any version
of the shared library that satisfies that dependency.

As zlib1g also provides a udeb containing the shared library, there
would also be a second line:

   udeb: libz 1 zlib1g-udeb (>= 1:1.2.3.3.dfsg)


8.6.4.3. Providing a "shlibs" file
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To provide a "shlibs" file for a shared library binary package, create
a "shlibs" file following the format described above and place it in
the "DEBIAN" directory for that package during the build. It will then
be included as a control file for that package.  [22]

Since "dpkg-shlibdeps" reads the "DEBIAN/shlibs" files in all of the
binary packages being built from this source package, all of the
"DEBIAN/shlibs" files should be installed before "dpkg-shlibdeps" is
called on any of the binary packages.

[22] This is what "dh_makeshlibs" in the debhelper suite does. If your
     package also has a udeb that provides a shared library,
     "dh_makeshlibs" can automatically generate the "udeb:" lines if
     you specify the name of the udeb with the "--add-udeb" option.



9. The Operating System
***********************


9.1. File system hierarchy
==========================


9.1.1. File System Structure
----------------------------

The location of all files and directories must comply with the
Filesystem Hierarchy Standard (FHS), version 3.0, with the exceptions
noted below, and except where doing so would violate other terms of
Debian Policy. The following exceptions to the FHS apply:

1. The FHS requirement that architecture-independent application-
   specific static files be located in "/usr/share" is relaxed to a
   suggestion. In particular, a subdirectory of "/usr/lib" may be used
   by a package (or a collection of packages) to hold a mixture of
   architecture-independent and architecture-dependent files. However,
   when a directory is entirely composed of architecture-independent
   files, it should be located in "/usr/share".

2. The optional rules related to user specific configuration files for
   applications are stored in the user's home directory are relaxed.
   It is recommended that such files start with the '"."' character (a
   "dot file"), and if an application needs to create more than one
   dot file then the preferred placement is in a subdirectory with a
   name starting with a '.' character, (a "dot directory"). In this
   case it is recommended the configuration files not start with the
   '.' character.

3. Only the dynamic linker and libc are allowed to install files in
   "/lib64".

4. The requirement for object files, internal binaries, and libraries,
   including "libc.so.*", to be located directly under "/lib{,32}" and
   "/usr/lib{,32}" is amended, permitting files to instead be
   installed to "/lib/triplet" and "/usr/lib/triplet", where "triplet"
   is the value returned by "dpkg-architecture -qDEB_HOST_MULTIARCH"
   for the architecture of the package. Packages must not install
   files to any triplet path other than the one matching the
   architecture of that package; for instance, an "Architecture:
   amd64" package containing 32-bit x86 libraries must not install
   these libraries to "/usr/lib/i386-linux-gnu".  [1]

   Packages for 64-bit architectures must not install files in
   "/usr/lib64" or in a subdirectory of it.

   The requirement for C and C++ headers files to be accessible
   through the search path "/usr/include/" is amended, permitting
   files to be accessible through the search path
   "/usr/include/triplet" where "triplet" is as above.  [2]

   Applications may also use a single subdirectory under
   "/usr/lib/triplet".

   The execution time linker/loader, ld*, must still be made available
   in the existing location under /lib or /lib64 since this is part of
   the ELF ABI for the architecture.

5. The requirement that "/usr/local/share/man" be "synonymous" with
   "/usr/local/man" is relaxed to a recommendation

6. The requirement that window managers with a single configuration
   file call it "system.*wmrc" is removed, as is the restriction that
   the window manager subdirectory be named identically to the window
   manager name itself.

7. The requirement that boot manager configuration files live in
   "/etc", or at least are symlinked there, is relaxed to a
   recommendation.

8. "/var/run" is required to be a symbolic link to "/run", and
   "/var/lock" is required to be a symbolic link to "/run/lock".

9. The "/var/www" directory is additionally allowed.

10. The requirement for "/usr/local/share/color" to exist if
    "/usr/share/color" exists is relaxed to a recommendation.

11. The requirement for "/usr/local/libqual" to exist if "/libqual" or
    "/usr/libqual" exists (where "libqual" is a variant of "lib" such
    as "lib32" or "lib64") is removed.

12. On GNU/Hurd systems, the following additional directories are
    allowed in the root filesystem: "/hurd" and "/servers".  [3]

13. As an exception to the requirement for there to be no
    subdirectories in "/usr/bin", the "mh" mail-handling suite may
    create "/usr/bin/mh/", as was allowed in FHS version 2.3. Other
    subdirectories are not allowed.

The version of this document referred here can be found in the
"debian-policy" package or on FHS (Debian copy) alongside this manual
(or, if you have the debian-policy installed, you can try FHS (local
copy)). The latest version, which may be a more recent version, may be
found on FHS (upstream). Specific questions about following the
standard may be asked on the "debian-devel" mailing list, or referred
to the FHS mailing list (see the FHS web site for more information).


9.1.2. Site-specific programs
-----------------------------

As mandated by the FHS, packages must not place any files in
"/usr/local", either by putting them in the file system archive to be
unpacked by "dpkg" or by manipulating them in their maintainer
scripts.

However, the package may create empty directories below "/usr/local"
so that the system administrator knows where to place site-specific
files. These are not directories *in* "/usr/local", but are children
of directories in "/usr/local". These directories
("/usr/local/*/dir/") should be removed on package removal if they are
empty.

Note that this applies only to directories *below* "/usr/local", not
*in* "/usr/local". Packages must not create sub-directories in the
directory "/usr/local" itself, except those listed in FHS, section
4.9. However, you may create directories below them as you wish. You
must not remove any of the directories listed in 4.9, even if you
created them.

If "/etc/staff-group-for-usr-local" does not exist, "/usr/local" and
all subdirectories created by packages should have permissions 0755
and be owned by "root:root".  If "/etc/staff-group-for-usr-local"
exists, "/usr/local" and subdirectories should have permissions 2775
(group-writable and set-group-id) and be owned by "root:staff".

Since "/usr/local" can be mounted read-only from a remote server,
"/usr/local/*/dir/" directories must be created and removed by the
"postinst" and "prerm" maintainer scripts and not be included in the
".deb" archive. These scripts must not fail if either of these
operations fail.

For example, the "emacsen-common" package could contain something like

   if [ ! -e /usr/local/share/emacs ]; then
       if mkdir /usr/local/share/emacs 2>/dev/null; then
           if test -e /etc/staff-group-for-usr-local ; then
               if chown root:staff /usr/local/share/emacs; then
                   chmod 2775 /usr/local/share/emacs || true
               fi
           elif chown root:root /usr/local/share/emacs; then
               chmod 0755 /usr/local/share/emacs || true
           fi
       fi
   fi

in its "postinst" script, and

   rmdir /usr/local/share/emacs/site-lisp 2>/dev/null || true
   rmdir /usr/local/share/emacs 2>/dev/null || true

in the "prerm" script. (Note that this form is used to ensure that if
the script is interrupted, the directory "/usr/local/share/emacs" will
still be removed.)

If you do create a directory in "/usr/local" for local additions to a
package, you should ensure that settings in "/usr/local" take
precedence over the equivalents in "/usr".

However, because "/usr/local" and its contents are for exclusive use
of the local administrator, a package must not rely on the presence or
absence of files or directories in "/usr/local" for normal operation.


9.1.3. The system-wide mail directory
-------------------------------------

The system-wide mail directory is "/var/mail". This directory is part
of the base system and should not be owned by any particular mail
agents. The use of the old location "/var/spool/mail" is deprecated,
even though the spool may still be physically located there.


9.1.4. "/run" and "/run/lock"
-----------------------------

The directory "/run" is cleared at boot, normally by being a mount
point for a temporary file system. Packages therefore must not assume
that any files or directories under "/run" other than "/run/lock"
exist unless the package has arranged to create those files or
directories since the last reboot. Normally, this is done by the
package via an init script. See Writing the scripts for more
information.

Packages must not include files or directories under "/run", or under
the older "/var/run" and "/var/lock" paths. The latter paths will
normally be symlinks or other redirections to "/run" for backwards
compatibility.


9.2. Users and groups
=====================


9.2.1. Introduction
-------------------

The Debian system can be configured to use either plain or shadow
passwords.

Some user ids (UIDs) and group ids (GIDs) are reserved globally for
use by certain packages. Because some packages need to include files
which are owned by these users or groups, or need the ids compiled
into binaries, these ids must be used on any Debian system only for
the purpose for which they are allocated. This is a serious
restriction, and we should avoid getting in the way of local
administration policies. In particular, many sites allocate users
and/or local system groups starting at 100.

Apart from this we should have dynamically allocated ids, which should
by default be arranged in some sensible order, but the behavior should
be configurable. When maintainers choose a new hardcoded or
dynamically generated username for packages to use, they should start
this username with an underscore. This minimizes collisions with
locally created user accounts.

Packages other than "base-passwd" must not modify "/etc/passwd",
"/etc/shadow", "/etc/group" or "/etc/gshadow".


9.2.2. UID and GID classes
--------------------------

The UID and GID numbers are divided into classes as follows:

0-99:
   Globally allocated by the Debian project, the same on every Debian
   system. These ids will appear in the "passwd" and "group" files of
   all Debian systems, new ids in this range being added automatically
   as the "base-passwd" package is updated.

   Packages which need a single statically allocated uid or gid should
   use one of these; their maintainers should ask the "base-passwd"
   maintainer for ids.

100-999:
   Dynamically allocated system users and groups. Packages which need
   a user or group, but can have this user or group allocated
   dynamically and differently on each system, should use "adduser
   --system" to create the group and/or user. "adduser" will check for
   the existence of the user or group, and if necessary choose an
   unused id based on the ranges specified in "adduser.conf".

1000-59999:
   Dynamically allocated user accounts. By default "adduser" will
   choose UIDs and GIDs for user accounts in this range, though
   "adduser.conf" may be used to modify this behavior.

60000-64999:
   Globally allocated by the Debian project, but only created on
   demand. The ids are allocated centrally and statically, but the
   actual accounts are only created on users' systems on demand.

   These ids are for packages which are obscure or which require many
   statically-allocated ids. These packages should check for and
   create the accounts in "/etc/passwd" or "/etc/group" (using
   "adduser" if it has this facility) if necessary. Packages which are
   likely to require further allocations should have a "hole" left
   after them in the allocation, to give them room to grow.

65000-65533:
   Reserved.

65534:
   User "nobody". The corresponding gid refers to the group "nogroup".

65535:
   This value *must not* be used, because it was the error return
   sentinel value when "uid_t" was 16 bits.

65536-99999, 600100001-4294967293:
   Dynamically allocated user accounts. By default "adduser" will not
   allocate UIDs and GIDs in this range, to ease compatibility with
   legacy systems where "uid_t" is still 16 bits.

100000-600100000:
   Dynamically allocated subordinate user ids. See subuid(5).
   "useradd" in its default configuration (and thus "adduser")
   automatically allocates a range of 65536 of these to each new non-
   system user created.

4294967294:
   "(uid_t)(-2) == (gid_t)(-2)" *must not* be used, because it is used
   as the anonymous, unauthenticated user by some NFS implementations.

4294967295:
   "(uid_t)(-1) == (gid_t)(-1)" *must not* be used, because it is the
   error return sentinel value.


9.2.3. Non-existent home directories
------------------------------------

The canonical non-existent home directory is "/nonexistent".  Users
who should not have a home directory should have their home directory
set to this value.

The Debian autobuilders set HOME to "/nonexistent" so that packages
which try to write to a home directory will fail to build.


9.3. Starting system services
=============================

Debian packages that provide system services should arrange for those
services to be automatically started and stopped by the init system or
service manager.  This section describes how that is done.


9.3.1. Introduction
-------------------

The default init system and service manager in Debian is "systemd".
Packages that wish to automatically start and stop system services
must include "systemd" service units to do so, unless the service is
only intended for use on systems running alternate init systems.  See
*systemd.service(5)* for details on the syntax of a service unit file.

In the common case that a package includes a single system service,
the service unit should have the same name as the package plus the
".service" extension.

Packages including a service unit may optionally include an init
script to support other init systems.  In this case, the init script
should have the same name as the "systemd" service unit so that
"systemd" will ignore it and use the service unit instead.  Packages
may also support other init systems by including configuration in the
native format of those init systems.

"systemd" uses dependency and ordering information contained within
the enabled unit files to decide which services to run and in which
order. The "sysv-rc" runlevel system for "sysvinit" uses symlinks in
"/etc/rcn.d" to decide which scripts to run and in which order at boot
time and when the init state (or "runlevel") is changed.  See the
"README.runlevels" file shipped with "sysv-rc" for implementation
details.  Other alternatives might exist.

The sections below describe how to write those scripts and configure
those symlinks.


9.3.2. Writing the scripts
--------------------------

Init scripts are placed in "/etc/init.d".  In the common case that a
package starts a single service, they should be named
"/etc/init.d/package".  They should accept one argument, saying what
to do:

"start"
   start the service,

"stop"
   stop the service,

"restart"
   stop and restart the service if it's already running, otherwise
   start the service

"try-restart"
   restart the service if it's already running, otherwise just report
   success.

"reload"
   cause the configuration of the service to be reloaded without
   actually stopping and restarting the service,

"force-reload"
   cause the configuration to be reloaded if the service supports
   this, otherwise restart the service.

"status"
   report the current status of the service

The "start", "stop", "restart", and "force-reload" options should be
supported by all init scripts. Supporting "status" is encouraged. The
"reload" and "try-restart" options are optional.

The "init.d" scripts must ensure that they will behave sensibly (i.e.,
returning success and not starting multiple copies of a service) if
invoked with "start" when the service is already running, or with
"stop" when it isn't, and that they don't kill unfortunately-named
user processes. The best way to achieve this is usually to use "start-
stop-daemon" with the "--oknodo" option.

Be careful of using "set -e" in "init.d" scripts. Writing correct
"init.d" scripts requires accepting various error exit statuses when
daemons are already running or already stopped without aborting the
"init.d" script, and common "init.d" function libraries are not safe
to call with "set -e" in effect.  [4] For "init.d" scripts, it's often
easier to not use "set -e" and instead check the result of each
command separately.

If a service reloads its configuration automatically (as in the case
of "cron", for example), the "reload" option of the "init.d" script
should behave as if the configuration has been reloaded successfully.

The "/etc/init.d" scripts must be treated as configuration files,
either (if they are present in the package, that is, in the .deb file)
by marking them as "conffile"s, or, (if they do not exist in the .deb)
by managing them correctly in the maintainer scripts (see
Configuration files). This is important since we want to give the
local system administrator the chance to adapt the scripts to the
local system, e.g., to disable a service without de-installing the
package, or to specify some special command line options when starting
a service, while making sure their changes aren't lost during the next
package upgrade.

These scripts should not fail obscurely when the configuration files
remain but the package has been removed, as configuration files remain
on the system after the package has been removed. Only when "dpkg" is
executed with the "--purge" option will configuration files be
removed. In particular, as the "/etc/init.d/package" script itself is
usually a "conffile", it will remain on the system if the package is
removed but not purged. Therefore, you should include a "test"
statement at the top of the script, like this:

   test -f program-executed-later-in-script || exit 0

Often there are some variables in the "init.d" scripts whose values
control the behavior of the scripts, and which a system administrator
is likely to want to change. As the scripts themselves are frequently
"conffile"s, modifying them requires that the administrator merge in
their changes each time the package is upgraded and the "conffile"
changes. To ease the burden on the system administrator, such
configurable values should not be placed directly in the script.
Instead, they should be placed in a file in "/etc/default", which
typically will have the same base name as the "init.d" script. This
extra file should be sourced by the script when the script runs. It
must contain only variable settings and comments in POSIX.1-2017 "sh"
format. It must either be a "conffile" or a configuration file
maintained by the package maintainer scripts. See Configuration files
for more details.

To ensure that vital configurable values are always available, the
"init.d" script should set default values for each of the shell
variables it uses, either before sourcing the "/etc/default/" file or
afterwards using something like the ": ${VAR:=default}" syntax. Also,
the "init.d" script must behave sensibly and not fail if the
"/etc/default" file is deleted.

Files and directories under "/run", including ones referred to via the
compatibility paths "/var/run" and "/var/lock", are normally stored on
a temporary filesystem and are normally not persistent across a
reboot. The "init.d" scripts must handle this correctly. This will
typically mean creating any required subdirectories dynamically when
the "init.d" script is run. See /run and /run/lock for more
information.


9.3.3. Interfacing with init systems
------------------------------------

Maintainer scripts for packages including init scripts must use
"update-rc.d" as described below to interact with the service manager
for requests such as enabling or disabling services.  They should use
"invoke-rc.d" as described below to invoke init scripts for requests
such as starting and stopping service.

Directly managing the "/etc/rc?.d" links and directly invoking the
"/etc/init.d/" init scripts should be done only by packages providing
the init script subsystem (such as "init-system-helpers").


9.3.3.1. Managing the links
~~~~~~~~~~~~~~~~~~~~~~~~~~~

The program "update-rc.d" is provided for package maintainers to
arrange for the proper creation and removal of "/etc/rcn.d" symbolic
links, or their functional equivalent if another method is being used.
It is intended for use in package maintainer scripts.

You must not include any "/etc/rcn.d" symbolic links in the actual
archive or manually create or remove the symbolic links in maintainer
scripts; you must use the "update-rc.d" program instead. (The former
will fail if an alternative method of maintaining runlevel information
is being used.) You must not include the "/etc/rcn.d" directories
themselves in the archive either. (Only the "init-system-helpers"
package is permitted to do so.)

To get the default behavior for your package, put in your "postinst"
script:

   update-rc.d package defaults

and in your "postrm":

   if [ "$1" = purge ]; then
       update-rc.d package remove
   fi

The default behaviour is to enable autostarting your package's daemon.
The local administrator can override this using the command "update-
rc.d package disable".  If, however, the daemon should not be
autostarted unless the local administrator has explicitly requested
this, instead add to your "postinst" script:

   update-rc.d package defaults-disabled

and add a dependency on "init-system-helpers (>= 1.50)", which
introduced the "defaults-disabled" option.  Then the local
administrator can enable autostarting the daemon using the command
"update-rc.d package enable".

An older practice, which should not be used, was to include a line
like "DISABLED=yes" in the package's "/etc/default" file.  The
package's init script would not start the service until the local
system administrator changed this to "DISABLED=no", or similar.  The
problem with this approach was that it hides from the init system
whether or not the daemon should actually be started, which leads to
inconsistent and confusing behavior: "service <package> start" could
return success but not start the service; services with a dependency
on this service will be started even though the service isn't running;
and init system status commands could incorrectly claim that the
service was started.

Note that if your package changes runlevels or priority, you may have
to remove and recreate the links, since otherwise the old links may
persist. Refer to the documentation of "update-rc.d".

For more information about using "update-rc.d", please consult its man
page, *update-rc.d(8)*.

It is easiest for packages not to call "update-rc.d" directly, but
instead use debhelper programs that add the required "update-rc.d"
calls automatically. See "dh_installinit", "dh_installsystemd", etc.


9.3.3.2. Running init scripts
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The program "invoke-rc.d" is provided to make it easier for package
maintainers to properly invoke an init script, obeying runlevel and
other locally-defined constraints that might limit a package's right
to start, stop and otherwise manage services. This program may be used
by maintainers in their packages' scripts.

The package maintainer scripts must use "invoke-rc.d" to invoke the
"/etc/init.d/*" init scripts or equivalent instead of calling them
directly.

By default, "invoke-rc.d" will pass any action requests (start, stop,
reload, restart...) to the "/etc/init.d" script, filtering out
requests to start or restart a service out of its intended runlevels.

Most packages will simply use:

   invoke-rc.d package action

in their "postinst" and "prerm" scripts.

A package should register its init script services using "update-rc.d"
before it tries to invoke them using "invoke-rc.d". Invocation of
unregistered services may fail.

For more information about using "invoke-rc.d", please consult its man
page, *invoke-rc.d(8)*.

It is easiest for packages not to call "invoke-rc.d" directly, but
instead use debhelper programs that add the required "invoke-rc.d"
calls automatically. See "dh_installinit", "dh_installsystemd", etc.


9.3.4. Boot-time initialization
-------------------------------

This section has been deleted.


9.3.5. Example
--------------

Examples on which you can base your "systemd" service units are
available in the man page *systemd.unit(5)*. An example on which you
can base your init scripts is available in the man page
*init-d-script(5)*.


9.4. Console messages from "init.d" scripts
===========================================

This section has been deleted.


9.5. Cron jobs
==============

Packages must not modify the configuration file "/etc/crontab", and
they must not modify the files in "/var/spool/cron/crontabs".

If a package wants to install a job that has to be executed via cron,
it should place a file named as specified in Cron job file names into
one or more of the following directories:

* "/etc/cron.hourly"

* "/etc/cron.daily"

* "/etc/cron.weekly"

* "/etc/cron.monthly"

As these directory names imply, the files within them are executed on
an hourly, daily, weekly, or monthly basis, respectively. The exact
times are listed in "/etc/crontab".

All files installed in any of these directories must be scripts (e.g.,
shell scripts or Perl scripts) so that they can easily be modified by
the local system administrator. In addition, they must be treated as
configuration files.

If a certain job has to be executed at some other frequency or at a
specific time, the package should install a file in "/etc/cron.d" with
a name as specified in Cron job file names. This file uses the same
syntax as "/etc/crontab" and is processed by "cron" automatically. The
file must also be treated as a configuration file. (Note that entries
in the "/etc/cron.d" directory are not handled by "anacron". Thus, you
should only use this directory for jobs which may be skipped if the
system is not running.)

Unlike "crontab" files described in the IEEE Std 1003.1-2008 (POSIX.1)
available from The Open Group, the files in "/etc/cron.d" and the file
"/etc/crontab" have seven fields; namely:

1. Minute [0,59]

2. Hour [0,23]

3. Day of the month [1,31]

4. Month of the year [1,12]

5. Day of the week ([0,6] with 0=Sunday)

6. Username

7. Command to be run

Ranges of numbers are allowed. Ranges are two numbers separated with a
hyphen. The specified range is inclusive. Lists are allowed. A list is
a set of numbers (or ranges) separated by commas. Step values can be
used in conjunction with ranges.

The scripts or "crontab" entries in these directories should check if
all necessary programs are installed before they try to execute them.
Otherwise, problems will arise when a package was removed but not
purged since configuration files are kept on the system in this
situation.

Any "cron" daemon must provide "/usr/bin/crontab" and support normal
"crontab" entries as specified in POSIX. The daemon must also support
names for days and months, ranges, and step values. It has to support
"/etc/crontab", and correctly execute the scripts in "/etc/cron.d".
The daemon must also correctly execute scripts in
"/etc/cron.{hourly,daily,weekly,monthly}".


9.5.1. Cron job file names
--------------------------

The file name of a cron job file should normally match the name of the
package from which it comes.

If a package supplies multiple cron job files files in the same
directory, the file names should all start with the name of the
package (possibly modified as described below) followed by a hyphen
("-") and a suitable suffix.

A cron job file name must not include any period or plus characters
("." or "+") characters as this will cause cron to ignore the file.
Underscores ("_") should be used instead of "." and "+" characters.


9.6. Menus
==========

Packages shipping applications that comply with minimal requirements
described below for integration with desktop environments should
register these applications in the desktop menu, following the
*FreeDesktop* standard, using text files called *desktop entries*.
Their format is described in the *Desktop Entry Specification* at
https://standards.freedesktop.org/desktop-entry-spec/latest/ and
complementary information can be found in the *Desktop Menu
Specification* at https://standards.freedesktop.org/menu-spec/latest/.

The desktop entry files are installed by the packages in the directory
"/usr/share/applications" and the FreeDesktop menus are refreshed
using *dpkg triggers*. It is therefore not necessary to depend on
packages providing FreeDesktop menu systems.

Entries displayed in the FreeDesktop menu should conform to the
following minima for relevance and visual integration.

* Unless hidden by default, the desktop entry must point to a PNG or
  SVG icon with a transparent background, providing at least the 22×22
  size, and preferably up to 64×64. The icon should be neutral enough
  to integrate well with the default icon themes. It is encouraged to
  ship the icon in the default *hicolor* icon theme directories, or to
  use an existing icon from the *hicolor* theme.

* If the menu entry is not useful in the general case as a standalone
  application, the desktop entry should set the "NoDisplay" key to
  true, so that it can be configured to be displayed only by those who
  need it.

* In doubt, the package maintainer should coordinate with the
  maintainers of menu implementations through the *debian-desktop*
  mailing list in order to avoid problems with categories or bad
  interactions with other icons. Especially for packages which are
  part of installation tasks, the contents of the
  "NotShowIn"/"OnlyShowIn" keys should be validated by the maintainers
  of the relevant environments.

Since the FreeDesktop menu is a cross-distribution standard, the
desktop entries written for Debian should be forwarded upstream, where
they will benefit to other users and are more likely to receive extra
contributions such as translations.

If a package installs a FreeDesktop desktop entry, it must not also
install a Debian menu entry.


9.7. Multimedia handlers
========================

Media types (formerly known as MIME types, Multipurpose Internet Mail
Extensions, RFCs 2045-2049) is a mechanism for encoding files and data
streams and providing meta-information about them, in particular their
type and format (e.g. "image/png", "text/html", "audio/ogg").

Registration of media type handlers allows programs like mail user
agents and web browsers to invoke these handlers to view, edit or
display media types they don't support directly.

There are two overlapping systems to associate media types to programs
which can handle them. The *mailcap* system is found on a large number
of Unix systems. The *FreeDesktop* system is aimed at Desktop
environments. In Debian, FreeDesktop entries are automatically
translated in mailcap entries, therefore packages already using
desktop entries should not use the mailcap system directly.


9.7.1. Registration of media type handlers with desktop entries
---------------------------------------------------------------

Packages shipping an application able to view, edit or point to files
of a given media type, or open links with a given URI scheme, should
list it in the "MimeType" key of the application's desktop entry. For
URI schemes, the relevant MIME types are "x-scheme-handler/*" (e.g. "x
-scheme-handler/https").


9.7.2. Registration of media type handlers with mailcap entries
---------------------------------------------------------------

Packages that are not using desktop entries for registration should
install a file in *mailcap(5)* format (RFC 1524) in the directory
"/usr/lib/mime/packages/". The file name should be the binary
package's name.

The mailcap package provides the "update-mime" program, which
integrates these registrations in the "/etc/mailcap" file, using dpkg
triggers.  [5]

Packages installing desktop entries should not install mailcap entries
for the same program, because the mailcap package already reads
desktop entries.

Packages using these facilities *should not* depend on, recommend, or
suggest "mailcap".


9.7.3. Providing media types to files
-------------------------------------

The media type of a file is discovered by inspecting the file's
extension or its *magic(5)* pattern, and interrogating a database
associating them with media types.

To support new associations between media types and files, their
characteristic file extensions and magic patterns should be registered
to the IANA (Internet Assigned Numbers Authority). See
https://www.iana.org/assignments/media-types and RFC 6838 for details.
This information will then propagate to the systems discovering file
media types in Debian, provided by the shared-mime-info, media-types
and file packages. If registration and propagation can not be waited
for, support can be asked to the maintainers of the packages mentioned
above.

For files that are produced and read by a single application, it is
also possible to declare this association to the *Shared MIME Info*
system by installing in the directory "/usr/share/mime/packages" a
file in the XML format specified at https://standards.freedesktop.org
/shared-mime-info-spec/latest/.


9.8. Keyboard configuration
===========================

To achieve a consistent keyboard configuration so that all
applications interpret a keyboard event the same way, all programs in
the Debian distribution must be configured to comply with the
following guidelines.

The following keys must have the specified interpretations:

"<--"
   delete the character to the left of the cursor

"Delete"
   delete the character to the right of the cursor

"Control+H"
   emacs: the help prefix

The interpretation of any keyboard events should be independent of the
terminal that is used, be it a virtual console, an X terminal
emulator, an rlogin/telnet session, etc.

The following list explains how the different programs should be set
up to achieve this:

* "<--" generates "KB_BackSpace" in X.

* "Delete" generates "KB_Delete" in X.

* X translations are set up to make "KB_Backspace" generate ASCII DEL,
  and to make "KB_Delete" generate "ESC [ 3 ~" (this is the vt220
  escape code for the "delete character" key). This must be done by
  loading the X resources using "xrdb" on all local X displays, not
  using the application defaults, so that the translation resources
  used correspond to the "xmodmap" settings.

* The Linux console is configured to make "<--" generate DEL, and
  "Delete" generate "ESC [ 3 ~".

* X applications are configured so that "<" deletes left, and "Delete"
  deletes right. Motif applications already work like this.

* Terminals should have "stty erase ^?" .

* The "xterm" terminfo entry should have "ESC [ 3 ~" for "kdch1", just
  as for "TERM=linux" and "TERM=vt220".

* Emacs is programmed to map "KB_Backspace" or the "stty erase"
  character to "delete-backward-char", and "KB_Delete" or "kdch1" to
  "delete-forward-char", and "^H" to "help" as always.

* Other applications use the "stty erase" character and "kdch1" for
  the two delete keys, with ASCII DEL being "delete previous
  character" and "kdch1" being "delete character under cursor".

This will solve the problem except for the following cases:

* Some terminals have a "<--" key that cannot be made to produce
  anything except "^H". On these terminals Emacs help will be
  unavailable on "^H" (assuming that the "stty erase" character takes
  precedence in Emacs, and has been set correctly). "M-x help" or "F1"
  (if available) can be used instead.

* Some operating systems use "^H" for "stty erase". However, modern
  telnet versions and all rlogin versions propagate "stty" settings,
  and almost all UNIX versions honour "stty erase". Where the "stty"
  settings are not propagated correctly, things can be made to work by
  using "stty" manually.

* Some systems (including previous Debian versions) use "xmodmap" to
  arrange for both "<--" and "Delete" to generate "KB_Delete". We can
  change the behavior of their X clients using the same X resources
  that we use to do it for our own clients, or configure our clients
  using their resources when things are the other way around. On
  displays configured like this "Delete" will not work, but "<--"
  will.

* Some operating systems have different "kdch1" settings in their
  "terminfo" database for "xterm" and others. On these systems the
  "Delete" key will not work correctly when you log in from a system
  conforming to our policy, but "<--" will.


9.9. Environment variables
==========================

Programs installed on the system PATH ("/bin", "/usr/bin", "/sbin",
"/usr/sbin", or similar directories) must not depend on custom
environment variable settings to get reasonable defaults. This is
because such environment variables would have to be set in a system-
wide configuration file such as a file in "/etc/profile.d", which is
not supported by all shells.

If a program usually depends on environment variables for its
configuration, the program should be changed to fall back to a
reasonable default configuration if these environment variables are
not present. If this cannot be done easily (e.g., if the source code
of a non-free program is not available), the program must be replaced
by a small "wrapper" shell script that sets the environment variables
if they are not already defined, and calls the original program.

Here is an example of a wrapper script for this purpose:

   #!/bin/sh
   BAR=${BAR:-/var/lib/fubar}
   export BAR
   exec /usr/lib/foo/foo "$@"


9.10. Registering Documents using doc-base
==========================================

The doc-base package implements a mechanism for handling and
presenting documentation. Debian packages that provides online
documentation (other than just manual pages) may register these
documents with doc-base by installing a doc-base control file in
"/usr/share/doc-base/".

Please refer to the documentation that comes with the doc-base package
for information and details.


9.11. Alternate init systems
============================

This section has been deleted.


9.11.1. Event-based boot with upstart
-------------------------------------

The "upstart" event-based boot system is no longer maintained in
Debian, so this section has been removed.

[1] This is necessary in order to reserve the directories for use in
    cross-installation of library packages from other architectures,
    as part of "multiarch".

[2] This is necessary for architecture-dependent headers file to
    coexist in a "multiarch" setup.

[3] These directories are used to store translators and as a set of
    standard names for mount points, respectively.

[4] "/lib/lsb/init-functions", which assists in writing LSB-compliant
    init scripts, may fail if "set -e" is in effect and echoing status
    messages to the console fails, for example.

[5] Creating, modifying or removing a file in
    "/usr/lib/mime/packages/" using maintainer scripts will not
    activate the trigger. In that case, it can be done by calling
    "dpkg-trigger --no-await /usr/lib/mime/packages" from the
    maintainer script after creating, modifying, or removing the file.


9.12. Signaling that a reboot is required
=========================================

Programs can signal that a reboot is required by "touch"ing "/run
/reboot-required".  It is conventional to add the name of the
package(s) requiring the reboot to "/run/reboot-required.pkgs".
Programs should not add a package name to "/run/reboot-required.pkgs"
if it is already present there.

The "/run/reboot-required" mechanism is used when a reboot is needed
to fully apply the changes introduced by package installation or
upgrade.  Typically it is the "postinst" maintainer script that
touches "/run/reboot-required", at the end of a successful
configuration of the package.

There are no guarantees provided by the "/run/reboot-required"
convention as to when or whether the requested reboot will occur.



10. Files
*********


10.1. Binaries
==============

Two different packages must not install programs with different
functionality but with the same filenames. This also applies when they
are installed into different directories on the default (user or root)
"PATH". (The case of two programs having the same functionality but
different implementations is handled via "alternatives" or the
"Conflicts" mechanism. See Maintainer Scripts and Conflicting binary
packages - Conflicts respectively.) If this case happens, one of the
programs must be renamed. The maintainers should report this to the
"debian-devel" mailing list and try to find a consensus about which
program will have to be renamed. If a consensus cannot be reached,
*both* programs must be renamed.

There is an exception to the above rules for "/usr/games": packages
that already install programs to "/usr/games", where another package
installs a program of the same name with different functionality to a
different directory on the default "PATH", may continue to do so.
However, packages must not install any newly conflicting programs to
"/usr/games", and packages already doing so are encouraged to move
these programs to non-conflicting names.

Packages must not install files to paths whose first component is a
name directly under the file system root and which is a symbolic link
to a directory of the same name under "/usr".  That is, packages must
not install files to paths matching the glob patterns "/bin/*",
"/lib/*", "/lib*/*" and "/sbin/*".  The base-files package is an
exception, for it installs aliasing symbolic links from "/bin" to
"/usr/bin", "/lib" to "/usr/lib", et cetera.  This restriction is
necessary to avoid triggering undefined behaviour in "dpkg".

Packages may assume that "/bin", "/lib" and "/sbin" are always
symbolic links such that files under "/usr/bin", "/usr/lib" and
"/usr/sbin" are always accessible via these aliases.

Binary executables must not be statically linked with the GNU C
library, since this prevents the binary from benefiting from fixes and
improvements to the C library without being rebuilt and complicates
security updates. This requirement may be relaxed for binary
executables whose intended purpose is to diagnose and fix the system
in situations where the GNU C library may not be usable (such as
system recovery shells or utilities like ldconfig) or for binary
executables where the security benefits of static linking outweigh the
drawbacks.

By default, when a package is being built, any binaries created should
include debugging information, as well as being compiled with
optimization. You should also turn on as many reasonable compilation
warnings as possible (see Main building script: debian/rules). For the
C programming language, this means the following compilation
parameters should be used:

   CC = gcc
   CFLAGS = -O2 -g -Wall # sane warning options vary between programs
   LDFLAGS = # none

By default all installed binaries should be stripped by calling

   strip --strip-unneeded --remove-section=.comment --remove-section=.note binaries

on the binaries after they have been copied into "debian/tmp" but
before the tree is made into a package.

It is not recommended to strip binaries by passing the "-s" flag to
"install", because this fails to remove .comment and .note sections,
and also prevents the automatic creation of dbgsym binary packages by
tools like "dh_strip".

Although binaries in the build tree should be compiled with debugging
information by default, it can often be difficult to debug programs if
they are also subjected to compiler optimization. For this reason, it
is recommended to support the standardized environment variable
"DEB_BUILD_OPTIONS" (see debian/rules and DEB_BUILD_OPTIONS). This
variable can contain several flags to change how a package is compiled
and built.

It is up to the package maintainer to decide what compilation options
are best for the package. Certain binaries (such as computationally-
intensive programs) will function better with certain flags ("-O3",
for example); feel free to use them. Please use good judgment here.
Don't use flags for the sake of it; only use them if there is good
reason to do so. Feel free to override the upstream author's ideas
about which compilation options are best: they are often inappropriate
for our environment.


10.2. Libraries
===============

If the package is **architecture: any**, then the shared library
compilation and linking flags must have "-fPIC", or the package shall
not build on some of the supported architectures.  [1] Any exception
to this rule must be discussed on the mailing list *debian-
devel@lists.debian.org*, and a rough consensus obtained. The reasons
for not compiling with "-fPIC" flag must be recorded in the file
"README.Debian", and care must be taken to either restrict the
architecture or arrange for "-fPIC" to be used on architectures where
it is required.  [2]

As to the static libraries, the common case is not to have relocatable
code, since there is no benefit, unless in specific cases; therefore
the static version must not be compiled with the "-fPIC" flag. Any
exception to this rule should be discussed on the mailing list
*debian-devel@lists.debian.org*, and the reasons for compiling with
the "-fPIC" flag must be recorded in the file "README.Debian".  [3]

In other words, if both a shared and a static library is being built,
each source unit ("*.c", for example, for C files) will need to be
compiled twice, for the normal case.

Libraries should be built with threading support and to be thread-safe
if the library supports this.

Although not enforced by the build tools, shared libraries must be
linked against all libraries that they use symbols from in the same
way that binaries are. This ensures the correct functioning of the
symbols and shlibs systems and guarantees that all libraries can be
safely opened with "dlopen()". Packagers may wish to use the gcc
option "-Wl,-z,defs" when building a shared library. Since this option
enforces symbol resolution at build time, a missing library reference
will be caught early as a fatal build error.

All installed shared libraries should be stripped with

   strip --strip-unneeded --remove-section=.comment --remove-section=.note your-lib

(The option "--strip-unneeded" makes "strip" remove only the symbols
which aren't needed for relocation processing.) Shared libraries can
function perfectly well when stripped, since the symbols for dynamic
linking are in a separate part of the ELF object file.  [4]

Note that under some circumstances it may be useful to install a
shared library unstripped, for example when building a separate
package to support debugging.  The debhelper "dh_strip" tool can
create such packages automatically.

Shared object files (often ".so" files) that are not public libraries,
that is, they are not meant to be linked to by third party executables
(binaries of other packages), should be installed in subdirectories of
the "/usr/lib" or "/usr/lib/triplet" directories (see the FHS for a
definition). Such files are exempt from the rules that govern ordinary
shared libraries, except that they must not be installed executable
and should be stripped. [5]

Packages that use "libtool" to create and install their shared
libraries install a file containing additional metadata (ending in
".la") alongside the library. For public libraries intended for use by
other packages, these files normally should not be included in the
Debian package, since the information they include is not necessary to
link with the shared library on Debian and can add unnecessary
additional dependencies to other programs or libraries.  [6] If the
".la" file is required for that library (if, for instance, it's loaded
via "libltdl" in a way that requires that meta-information), the
"dependency_libs" setting in the ".la" file should normally be set to
the empty string. If the shared library development package has
historically included the ".la", it must be retained in the
development package (with "dependency_libs" emptied) until all
libraries that depend on it have removed or emptied "dependency_libs"
in their ".la" files to prevent linking with those other libraries
using "libtool" from failing.

If the ".la" must be included, it should be included in the
development ("-dev") package, unless the library will be loaded by
"libtool"'s "libltdl" library. If it is intended for use with
"libltdl", the ".la" files must go in the run-time library package.

These requirements for handling of ".la" files do not apply to
loadable modules or libraries not installed in directories searched by
default by the dynamic linker. Packages installing loadable modules
will frequently need to install the ".la" files alongside the modules
so that they can be loaded by "libltdl". "dependency_libs" does not
need to be modified for libraries or modules that are not installed in
directories searched by the dynamic linker by default and not intended
for use by other packages.

You must make sure that you use only released versions of shared
libraries to build your packages; otherwise other users will not be
able to run your binaries properly. Producing source packages that
depend on unreleased compilers is also usually a bad idea.


10.3. Shared libraries
======================

This section has moved to Shared libraries.


10.4. Scripts
=============

All command scripts, including the package maintainer scripts inside
the package and used by "dpkg", should have a "#!" line naming the
shell to be used to interpret them.

In the case of Perl scripts this should be "#!/usr/bin/perl".

When scripts are installed into a directory in the system PATH, the
script name should not include an extension such as ".sh" or ".pl"
that denotes the scripting language currently used to implement it.

Shell scripts ("sh" and "bash") other than "init.d" scripts should
almost certainly start with "set -e" so that errors are detected.
"init.d" scripts are something of a special case, due to how
frequently they need to call commands that are allowed to fail, and it
may instead be easier to check the exit status of commands directly.
See Writing the scripts for more information about writing "init.d"
scripts.

Every script should use "set -e" or check the exit status of *every*
command.

Scripts may assume that "/bin/sh" implements the POSIX.1-2017 Shell
Command Language  [7] plus the following additional features not
mandated by POSIX.1-2017.. [8]

* "echo -n", if implemented as a shell built-in, must not generate a
  newline.

* "test", if implemented as a shell built-in, must support "-a" and
  "-o" as binary logical operators.

* "local" to create a scoped variable must be supported, including
  listing multiple variables in a single local command and assigning a
  value to a variable at the same time as localizing it. "local" may
  or may not preserve the variable value from an outer scope if no
  assignment is present. Uses such as:

     fname () {
         local a b c=delta d
         # ... use a, b, c, d ...
     }

  must be supported and must set the value of "c" to "delta".

* The XSI extension to "kill" allowing "kill -signal", where signal is
  either the name of a signal or one of the numeric signals listed in
  the XSI extension (0, 1, 2, 3, 6, 9, 14, and 15), must be supported
  if "kill" is implemented as a shell built-in.

* The XSI extension to "trap" allowing numeric signals must be
  supported. In addition to the signal numbers listed in the
  extension, which are the same as for "kill" above, 13 (SIGPIPE) must
  be allowed.

If a shell script requires non-POSIX.1-2017 features from the shell
interpreter other than those listed above, the appropriate shell must
be specified in the first line of the script (e.g., "#!/bin/bash") and
the package must depend on the package providing the shell (unless the
shell package is marked "Essential", as in the case of "bash").

You may wish to restrict your script to POSIX.1-2017 features plus the
above set when possible so that it may use "/bin/sh" as its
interpreter. Checking your script with "checkbashisms" from the
devscripts package or running your script with an alternate shell such
as "posh" may help uncover violations of the above requirements. If in
doubt whether a script complies with these requirements, use
"/bin/bash".

Perl scripts should check for errors when making any system calls,
including "open", "print", "close", "rename" and "system".

"csh" and "tcsh" should be avoided as scripting languages. See *Csh
Programming Considered Harmful*, one of the "comp.unix.*" FAQs, which
can be found at http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/.
If an upstream package comes with "csh" scripts then you must make
sure that they start with "#!/bin/csh" and make your package depend on
the "c-shell" virtual package.

Any scripts which create files in world-writeable directories (e.g.,
in "/tmp") must use a mechanism which will fail atomically if a file
with the same name already exists.

The Debian base system provides the "tempfile" and "mktemp" utilities
for use by scripts for this purpose.


10.5. Symbolic links
====================

In general, symbolic links within a top-level directory should be
relative, and symbolic links pointing from one top-level directory to
or into another should be absolute. (A top-level directory is a sub-
directory of the root directory "/".) For example, a symbolic link
from "/usr/lib/foo" to "/usr/share/bar" should be relative
("../share/bar"), but a symbolic link from "/var/run" to "/run" should
be absolute.  [9] Symbolic links must not traverse above the root
directory.

In addition, symbolic links should be specified as short as possible,
i.e., link targets like "foo/../bar" are deprecated.

Note that when creating a relative link using "ln" it is not necessary
for the target of the link to exist relative to the working directory
you're running "ln" from, nor is it necessary to change directory to
the directory where the link is to be made. Simply include the string
that should appear as the target of the link (this will be a pathname
relative to the directory in which the link resides) as the first
argument to "ln".

For example, in your "Makefile" or "debian/rules", you can do things
like:

   ln -fs gcc $(prefix)/bin/cc
   ln -fs gcc debian/tmp/usr/bin/cc
   ln -fs ../sbin/sendmail $(prefix)/bin/runq
   ln -fs ../sbin/sendmail debian/tmp/usr/bin/runq

A symbolic link pointing to a compressed file (in the sense that it is
meant to be uncompressed with "unzip" or "zless" etc.) should always
have the same file extension as the referenced file. (For example, if
a file "foo.gz" is referenced by a symbolic link, the filename of the
link has to end with "".gz"" too, as in "bar.gz".)


10.6. Device files
==================

Packages must not include device files or named pipes in the package
file tree.

Debian packages should assume that device files in "/dev" are
dynamically managed by the kernel or some other system facility and do
not have to be explicitly created or managed by the package. Debian
packages other than those whose purpose is to manage the "/dev" device
file tree must not attempt to create or remove device files in "/dev"
when a dynamic device management facility is in use.

If named pipes or device files outside of "/dev" are required by a
package, they should normally be created when necessary by the
programs in the package, by init scripts or systemd unit files, or by
similar on-demand mechanisms. If such files need to be created during
package installation, they must be created in the "postinst"
maintainer script [10] and removed in either the "prerm" or the
"postrm" maintainer script.


10.7. Configuration files
=========================


10.7.1. Definitions
-------------------

configuration file
   A file that affects the operation of a program, or provides site-
   or host-specific information, or otherwise customizes the behavior
   of a program. Typically, configuration files are intended to be
   modified by the system administrator (if needed or desired) to
   conform to local policy or to provide more useful site-specific
   behavior.

"conffile"
   A file listed in a package's "conffiles" file, and is treated
   specially by "dpkg" (see Details of configuration).

The distinction between these two is important; they are not
interchangeable concepts. Almost all "conffile"s are configuration
files, but many configuration files are not "conffiles".

As noted elsewhere, "/etc/init.d" scripts, "/etc/default" files,
scripts installed in "/etc/cron.{hourly,daily,weekly,monthly}", and
cron configuration installed in "/etc/cron.d" must be treated as
configuration files. In general, any script that embeds configuration
information is de-facto a configuration file and should be treated as
such.


10.7.2. Location
----------------

Any configuration files created or used by your package must reside in
"/etc". If there are several, consider creating a subdirectory of
"/etc" named after your package.

If your package creates or uses configuration files outside of "/etc",
and it is not feasible to modify the package to use "/etc" directly,
put the files in "/etc" and create symbolic links to those files from
the location that the package requires.


10.7.3. Behavior
----------------

Configuration file handling must conform to the following behavior:

* local changes must be preserved during a package upgrade, and

* configuration files must be preserved when the package is removed,
  and only deleted when the package is purged.

Obsolete configuration files without local changes should be removed
by the package during upgrade.  [11]

The easy way to achieve this behavior is to make the configuration
file a "conffile". This is appropriate only if it is possible to
distribute a default version that will work for most installations,
although some system administrators may choose to modify it. This
implies that the default version will be part of the package
distribution, and must not be modified by the maintainer scripts
during installation (or at any other time).

In order to ensure that local changes are preserved correctly,
packages must not contain or make hard links to conffiles. [12]

The other way to do it is via the maintainer scripts. In this case,
the configuration file must not be listed as a "conffile" and must not
be part of the package distribution. If the existence of a file is
required for the package to be sensibly configured it is the
responsibility of the package maintainer to provide maintainer scripts
which correctly create, update and maintain the file and remove it on
purge. (See Package maintainer scripts and installation procedure for
more information.) These scripts must be idempotent (i.e., must work
correctly if "dpkg" needs to re-run them due to errors during
installation or removal), must cope with all the variety of ways
"dpkg" can call maintainer scripts, must not overwrite or otherwise
mangle the user's configuration without asking, must not ask
unnecessary questions (particularly during upgrades), and must
otherwise be good citizens.

The scripts are not required to configure every possible option for
the package, but only those necessary to get the package running on a
given system. Ideally the sysadmin should not have to do any
configuration other than that done (semi-)automatically by the
"postinst" script.

A common practice is to create a script called "package-configure" and
have the package's "postinst" call it if and only if the configuration
file does not already exist. In certain cases it is useful for there
to be an example or template file which the maintainer scripts use.
Such files should be in "/usr/share/package" or "/usr/lib/package"
(depending on whether they are architecture-independent or not). There
should be symbolic links to them from
"/usr/share/doc/package/examples" if they are examples, and should be
perfectly ordinary "dpkg"-handled files (*not* configuration files).

These two styles of configuration file handling must not be mixed, for
that way lies madness: "dpkg" will ask about overwriting the file
every time the package is upgraded.


10.7.4. Sharing configuration files
-----------------------------------

If two or more packages use the same configuration file and it is
reasonable for both to be installed at the same time, one of these
packages must be defined as *owner* of the configuration file, i.e.,
it will be the package which handles that file as a configuration
file. Other packages that use the configuration file must depend on
the owning package if they require the configuration file to operate.
If the other package will use the configuration file if present, but
is capable of operating without it, no dependency need be declared.

If it is desirable for two or more related packages to share a
configuration file *and* for all of the related packages to be able to
modify that configuration file, then the following should be done:

1. One of the related packages (the "owning" package) will manage the
   configuration file with maintainer scripts as described in the
   previous section.

2. The owning package should also provide a program that the other
   packages may use to modify the configuration file.

3. The related packages must use the provided program to make any
   desired modifications to the configuration file. They should either
   depend on the core package to guarantee that the configuration
   modifier program is available or accept gracefully that they cannot
   modify the configuration file if it is not. (This is in addition to
   the fact that the configuration file may not even be present in the
   latter scenario.)

Sometimes it's appropriate to create a new package which provides the
basic infrastructure for the other packages and which manages the
shared configuration files. (The "sgml-base" package is a good
example.)

If the configuration file cannot be shared as described above, the
packages must be marked as conflicting with each other. Two packages
that specify the same file as a "conffile" must conflict. This is an
instance of the general rule about not sharing files. Neither
alternatives nor diversions are likely to be appropriate in this case;
in particular, "dpkg" does not handle diverted "conffile"s well.

When two packages both declare the same "conffile", they may see left-
over configuration files from each other even though they conflict
with each other. If a user removes (without purging) one of the
packages and installs the other, the new package will take over the
"conffile" from the old package. If the file was modified by the user,
it will be treated the same as any other locally modified "conffile"
during an upgrade.

The maintainer scripts must not alter a "conffile" of *any* package,
including the one the scripts belong to.


10.7.5. User configuration files ("dotfiles")
---------------------------------------------

The files in "/etc/skel" will automatically be copied into new user
accounts by "adduser". No other program should reference the files in
"/etc/skel".

Therefore, if a program needs a dotfile to exist in advance in "$HOME"
to work sensibly, that dotfile should be installed in "/etc/skel" and
treated as a configuration file.

However, programs that require dotfiles in order to operate sensibly
are a bad thing, unless they do create the dotfiles themselves
automatically.

Furthermore, programs should be configured by the Debian default
installation to behave as closely to the upstream default behavior as
possible.

Therefore, if a program in a Debian package needs to be configured in
some way in order to operate sensibly, that should be done using a
site-wide configuration file placed in "/etc". Only if the program
doesn't support a site-wide default configuration and the package
maintainer doesn't have time to add it may a default per-user file be
placed in "/etc/skel".

"/etc/skel" should be as empty as we can make it. This is particularly
true because there is no easy (or necessarily desirable) mechanism for
ensuring that the appropriate dotfiles are copied into the accounts of
existing users when a package is installed.


10.8. Log files
===============

Log files should usually be named "/var/log/package.log". If you have
many log files, or need a separate directory for permission reasons
("/var/log" is writable only by "root"), you should usually create a
directory named "/var/log/package" and place your log files there.

Log files must be rotated occasionally so that they don't grow
indefinitely. The best way to do this is to install a log rotation
configuration file in the directory "/etc/logrotate.d", normally named
"/etc/logrotate.d/package", and use the facilities provided by
"logrotate".  [13] Here is a good example for a logrotate config file
(for more information see *logrotate(8)*):

   /var/log/foo/*.log {
       rotate 12
       weekly
       compress
       missingok
       postrotate
           start-stop-daemon -K -p /var/run/foo.pid -s HUP -x /usr/sbin/foo -q
       endscript
   }

This rotates all files under "/var/log/foo", saves 12 compressed
generations, and tells the daemon to reopen its log files after the
log rotation. It skips this log rotation (via "missingok") if no such
log file is present, which avoids errors if the package is removed but
not purged.

Log files should be removed when the package is purged (but not when
it is only removed). This should be done by the "postrm" script when
it is called with the argument "purge" (see Details of removal and/or
configuration purging).


10.9. Locale files
==================

The directory "/usr/share/locale/" contains localization files for
different locales.

Packages should not require the existence of any files in
"/usr/share/locale/" in order to function in a "C" or "C.UTF-8"
locale.


10.10. Permissions and owners
=============================

The rules in this section are guidelines for general use. If necessary
you may deviate from the details below. However, if you do so you must
make sure that what is done is secure and you should try to be as
consistent as possible with the rest of the system. You are also
encouraged to discuss it on "debian-devel" first.

Files should be owned by "root:root", and made writable only by the
owner and universally readable (and executable, if appropriate), that
is mode 644 or 755.

Directories should be mode 755 or (for group-writability) mode 2775.
The ownership of the directory should be consistent with its mode: if
a directory is mode 2775, it should be owned by the group that needs
write access to it.  [14]

Control information files should be owned by "root:root" and either
mode 644 (for most files) or mode 755 (for executables such as
maintainer scripts).

Setuid and setgid executables should be mode 4755 or 2755
respectively, and owned by the appropriate user or group. They should
not be made unreadable (modes like 4711 or 2711 or even 4111); doing
so achieves no extra security, because anyone can find the binary in
the freely available Debian package; it is merely inconvenient. For
the same reason you should not restrict read or execute permissions on
non-set-id executables.

Some setuid programs need to be restricted to particular sets of
users, using file permissions. In this case they should be owned by
the uid to which they are set-id, and by the group which should be
allowed to execute them. They should have mode 4754; again there is no
point in making them unreadable to those users who must not be allowed
to execute them.

It is possible to arrange that the system administrator can
reconfigure the package to correspond to their local security policy
by changing the permissions on a binary: they can do this by using
"dpkg-statoverride", as described below.  [15] Another method you
should consider is to create a group for people allowed to use the
program(s) and make any setuid executables executable only by that
group.

If you need to create a new user or group for your package there are
two possibilities. Firstly, you may need to make some files in the
binary package be owned by this user or group, or you may need to
compile the user or group id (rather than just the name) into the
binary (though this latter should be avoided if possible, as in this
case you need a statically allocated id).

If you need a statically allocated id, you must ask for a user or
group id from the "base-passwd" maintainer, and must not release the
package until you have been allocated one. Once you have been
allocated one you must either make the package depend on a version of
the "base-passwd" package with the id present in "/etc/passwd" or
"/etc/group", or arrange for your package to create the user or group
itself with the correct id (using "adduser") in its "preinst" or
"postinst". (Doing it in the "postinst" is to be preferred if it is
possible, otherwise a pre-dependency will be needed on the "adduser"
package.)

On the other hand, the program might be able to determine the uid or
gid from the user or group name at runtime, so that a dynamically
allocated id can be used. In this case you should choose an
appropriate user or group name, discussing this on "debian-devel" and
checking that it is unique. When this has been checked you must
arrange for your package to create the user or group if necessary
using "adduser" in the "preinst" or "postinst" script (again, the
latter is to be preferred if it is possible).

Note that changing the numeric value of an id associated with a name
is very difficult, and involves searching the file system for all
appropriate files. You need to think carefully whether a static or
dynamic id is required, since changing your mind later will cause
problems.


10.10.1. The use of "dpkg-statoverride"
---------------------------------------

This section is not intended as policy, but as a description of the
use of "dpkg-statoverride".

If a system administrator wishes to have a file (or directory or other
such thing) installed with owner and permissions different from those
in the distributed Debian package, they can use the "dpkg-
statoverride" program to instruct "dpkg" to use the different settings
every time the file is installed. Thus the package maintainer should
distribute the files with their normal permissions, and leave it for
the system administrator to make any desired changes. For example, a
daemon which is normally required to be setuid root, but in certain
situations could be used without being setuid, should be installed
setuid in the ".deb". Then the local system administrator can change
this if they wish. If there are two standard ways of doing it, the
package maintainer can use "debconf" to find out the preference, and
call "dpkg-statoverride" in the maintainer script if necessary to
accommodate the system administrator's choice. Care must be taken
during upgrades to not override an existing setting.

Given the above, "dpkg-statoverride" is essentially a tool for system
administrators and would not normally be needed in the maintainer
scripts. There is one type of situation, though, where calls to "dpkg-
statoverride" would be needed in the maintainer scripts, and that
involves packages which use dynamically allocated user or group ids.
In such a situation, something like the following idiom can be very
helpful in the package's "postinst", where "sysuser" is a dynamically
allocated id:

   for i in /usr/bin/foo /usr/sbin/bar; do
       # only do something when no setting exists
       if ! dpkg-statoverride --list $i >/dev/null 2>&1; then
           #include: debconf processing, question about foo and bar
           if [ "$RET" = "true" ] ; then
               dpkg-statoverride --update --add sysuser root 4755 $i
           fi
       fi
   done

The corresponding code to remove the override when the package is
purged would be:

   for i in /usr/bin/foo /usr/sbin/bar; do
       if dpkg-statoverride --list $i >/dev/null 2>&1; then
           dpkg-statoverride --remove $i
       fi
   done


10.11. File names
=================

The name of the files installed by binary packages in the system PATH
(namely "/bin", "/sbin", "/usr/bin", "/usr/sbin" and "/usr/games")
must be encoded in ASCII.

The name of the files and directories installed by binary packages
outside the system PATH must be encoded in UTF-8 and should be
restricted to ASCII when it is possible to do so.

[1] If you are using GCC, "-fPIC" produces code with relocatable
    position independent code, which is required for most
    architectures to create a shared library, with i386 and perhaps
    some others where non position independent code is permitted in a
    shared library.

    Position independent code may have a performance penalty,
    especially on "i386". However, in most cases the speed penalty
    must be measured against the memory wasted on the few
    architectures where non position independent code is even
    possible.

[2] Some of the reasons why this might be required is if the library
    contains hand crafted assembly code that is not relocatable, the
    speed penalty is excessive for compute intensive libs, and similar
    reasons.

[3] Some of the reasons for linking static libraries with the "-fPIC"
    flag are if, for example, one needs a Perl API for a library that
    is under rapid development, and has an unstable API, so shared
    libraries are pointless at this phase of the library's
    development. In that case, since Perl needs a library with
    relocatable code, it may make sense to create a static library
    with relocatable code. Another reason cited is if you are
    distilling various libraries into a common shared library, like
    "mklibs" does in the Debian installer project.

[4] You might want to replace "--strip-unneeded" with "--strip-debug"
    for static libraries, as dh_strip does.  When stripping static
    libraries, you should also pass "--enable-deterministic-archives"
    to ensure that your package build is reproducible.

[5] A common example are the so-called "plug-ins", internal shared
    objects that are dynamically loaded by programs using *dlopen(3)*.

[6] These files store, among other things, all libraries on which that
    shared library depends. Unfortunately, if the ".la" file is
    present and contains that dependency information, using "libtool"
    when linking against that library will cause the resulting program
    or library to be linked against those dependencies as well, even
    if this is unnecessary. This can create unneeded dependencies on
    shared library packages that would otherwise be hidden behind the
    library ABI, and can make library transitions to new SONAMEs
    unnecessarily complicated and difficult to manage.

[7] The Open Group Base Specifications Issue 7, 2018 Edition, which is
    also known as POSIX.1-2017 and as IEEE Std 1003.1-2017 and is
    available on the World Wide Web from The Open Group.

[8] These features are in widespread use in the Linux community and
    are implemented in all of bash, dash, and ksh, the most common
    shells users may wish to use as "/bin/sh".

[9] This is necessary to allow top-level directories to be symlinks.
    If linking "/var/run" to "/run" were done with the relative
    symbolic link "../run", but "/var" were a symbolic link to
    "/srv/disk1", the symbolic link would point to "/srv/run" rather
    than the intended target.

[10] It's better to use "mkfifo" rather than "mknod" to create named
     pipes to avoid false positives from automated checks for packages
     incorrectly creating device files.

[11] The "dpkg-maintscript-helper" tool, available from the dpkg
     package, can help for this task.

[12] Rationale: There are two problems with hard links. The first is
     that some editors break the link while editing one of the files,
     so that the two files may unwittingly become unlinked and
     different. The second is that "dpkg" might break the hard link
     while upgrading "conffile"s.

[13] The traditional approach to log files has been to set up *ad hoc*
     log rotation schemes using simple shell scripts and cron. While
     this approach is highly customizable, it requires quite a lot of
     sysadmin work. Even though the original Debian system helped a
     little by automatically installing a system which can be used as
     a template, this was deemed not enough.

     The use of "logrotate", a program developed by Red Hat, is
     better, as it centralizes log management. It has both a
     configuration file ("/etc/logrotate.conf") and a directory where
     packages can drop their individual log rotation configurations
     ("/etc/logrotate.d").

[14] When a package is upgraded, and the owner or permissions of a
     file included in the package has changed, dpkg arranges for the
     ownership and permissions to be correctly set upon installation.
     However, this does not extend to directories; the permissions and
     ownership of directories already on the system does not change on
     install or upgrade of packages. This makes sense, since otherwise
     common directories like "/usr" would always be in flux. To
     correctly change permissions of a directory the package owns,
     explicit action is required, usually in the "postinst" script.
     Care must be taken to handle downgrades as well, in that case.

[15] Ordinary files installed by "dpkg" (as opposed to "conffile"s and
     other similar objects) normally have their permissions reset to
     the distributed permissions when the package is reinstalled.
     However, the use of "dpkg-statoverride" overrides this default
     behavior.



11. Customized programs
***********************


11.1. Architecture specification strings
========================================

If a program needs to specify an *architecture specification string*
in some place, it should select one of the strings provided by "dpkg-
architecture -L". The strings are in the format "os-arch", though the
OS part is sometimes elided, as when the OS is Linux.

Note that we don't want to use "arch-debian-linux" to apply to the
rule "architecture-vendor-os" since this would make our programs
incompatible with other Linux distributions. We also don't use
something like "arch-unknown-linux", since the "unknown" does not look
very good.


11.1.1. Architecture wildcards
------------------------------

A package may specify an architecture wildcard. Architecture wildcards
are in the format "any" (which matches every architecture), "os"-any,
or any-"cpu".  [1]


11.2. Daemons
=============

The configuration files "/etc/services", "/etc/protocols", and
"/etc/rpc" are managed by the "netbase" package and must not be
modified by other packages.

If a package requires a new entry in one of these files, the
maintainer should get in contact with the "netbase" maintainer, who
will add the entries and release a new version of the "netbase"
package.

The configuration file "/etc/inetd.conf" must not be modified by the
package's scripts except via the "update-inetd" script or the
"DebianNet.pm" Perl module. See their documentation for details on how
to add entries.

If a package wants to install an example entry into "/etc/inetd.conf",
the entry must be preceded with exactly one hash character ("#"). Such
lines are treated as "commented out by user" by the "update-inetd"
script and are not changed or activated during package updates.


11.3. Using pseudo-ttys and modifying wtmp, utmp and lastlog
============================================================

Some programs need to create pseudo-ttys. This should be done using
Unix98 ptys if the C library supports it. The resulting program must
not be installed setuid root, unless that is required for other
functionality.

The files "/var/run/utmp", "/var/log/wtmp" and "/var/log/lastlog" must
be installed writable by group "utmp". Programs which need to modify
those files must be installed setgid "utmp".


11.4. Editors and pagers
========================

Some programs have the ability to launch an editor or pager program to
edit or display a text document. Since there are lots of different
editors and pagers available in the Debian distribution, the system
administrator and each user should have the possibility to choose
their preferred editor and pager.

In addition, every program should choose a good default editor/pager
if none is selected by the user or system administrator.

Thus, every program that launches an editor or pager must use the
EDITOR or PAGER environment variable to determine the editor or pager
the user wishes to use. If these variables are not set, the programs
"/usr/bin/editor" and "/usr/bin/pager" should be used, respectively.
These commands may be invoked explicitly (e.g., as "/usr/bin/editor")
or via a PATH search (e.g., as "editor").

These two files are managed through the "dpkg" "alternatives"
mechanism. Every package providing an editor or pager must call the
"update-alternatives" script to register as an alternative for
"/usr/bin/editor" or "/usr/bin/pager" as appropriate. The alternative
should have a slave alternative for "/usr/share/man/man1/editor.1.gz"
or "/usr/share/man/man1/pager.1.gz" pointing to the corresponding
manual page.

If it is very hard to adapt a program to make use of the EDITOR or
PAGER variables, that program may be configured to use "/usr/bin
/sensible-editor" and "/usr/bin/sensible-pager" as the editor or pager
program respectively. These are two scripts provided in the sensible-
utils package that check the EDITOR and PAGER variables and launch the
appropriate program, and fall back to "/usr/bin/editor" and
"/usr/bin/pager" if the variable is not set.

A program may also use the VISUAL environment variable to determine
the user's choice of editor. If it exists, it should take precedence
over EDITOR. This is in fact what "/usr/bin/sensible-editor" does.

It is not required for a package to depend on "editor" and "pager",
nor is it required for a package to provide such virtual packages. [2]


11.5. Web servers and applications
==================================

This section describes the locations and URLs that should be used by
all web servers and web applications in the Debian system.

1. Cgi-bin executable files are installed in the directory

      /usr/lib/cgi-bin

   or a subdirectory of that directory, and the script

      /usr/lib/cgi-bin/.../cgi-bin-name

   should be referred to as

      http://localhost/cgi-bin/.../cgi-bin-name

2. (Deleted)

3. Access to images

   Images for a package should be stored in
   "/usr/share/images/package" and referred to through an alias
   "/images/" as:

      http://localhost/images/package/filename

4. Web Document Root

   Web Applications should try to avoid storing files in the Web
   Document Root. Instead they should use the /usr/share/doc/package
   directory for documents. If access to the web document root is
   unavoidable then use

      /var/www/html

   as the Document Root. This might be just a symbolic link to the
   location where the system administrator has put the real document
   root.

5. Providing httpd and/or httpd-cgi

   All web servers should provide the virtual package "httpd". If a
   web server has CGI support it should provide "httpd-cgi"
   additionally.

   All web applications which do not contain CGI scripts should depend
   on "httpd", all those web applications which "do" contain CGI
   scripts, should depend on "httpd-cgi".


11.6. Mail transport, delivery and user agents
==============================================

Debian packages which process electronic mail, whether mail user
agents (MUAs) or mail transport agents (MTAs), must ensure that they
are compatible with the configuration decisions below. Failure to do
this may result in lost mail, broken "From:" lines, and other serious
brain damage!

The mail spool is "/var/mail" and the interface to send a mail message
is "/usr/sbin/sendmail" (as per the FHS). On older systems, the mail
spool may be physically located in "/var/spool/mail", but all access
to the mail spool should be via the "/var/mail" symlink. The mail
spool is part of the base system and not part of the MTA package.

All Debian MUAs, MTAs, MDAs and other mailbox accessing programs (such
as IMAP daemons) must lock the mailbox in an NFS-safe way. This means
that "fcntl()" locking must be combined with dot locking. To avoid
deadlocks, a program should use "fcntl()" first and dot locking after
this, or alternatively implement the two locking methods in a non
blocking way.  [3] Using the functions "maillock" and "mailunlock"
provided by the "liblockfile*" packages is the recommended way to
accomplish this.

Mailboxes are generally either mode 600 and owned by user or mode 660
and owned by "user:mail".  [4] The local system administrator may
choose a different permission scheme; packages should not make
assumptions about the permission and ownership of mailboxes unless
required (such as when creating a new mailbox). A MUA may remove a
mailbox (unless it has nonstandard permissions) in which case the MTA
or another MUA must recreate it if needed.

The mail spool is 2775 "root:mail", and MUAs should be setgid mail to
do the locking mentioned above (and must obviously avoid accessing
other users' mailboxes using this privilege).

"/etc/aliases" is the source file for the system mail aliases (e.g.,
postmaster, usenet, etc.), it is the one which the sysadmin and
"postinst" scripts may edit. After "/etc/aliases" is edited the
program or human editing it must call "newaliases". All MTA packages
must come with a "newaliases" program, even if it does nothing, but
older MTA packages did not do this so programs should not fail if
"newaliases" cannot be found. Note that because of this, all MTA
packages must have "Provides", "Conflicts" and "Replaces:  mail-
transport-agent" control fields.

The convention of writing "forward to address" in the mailbox itself
is not supported. Use a ".forward" file instead.

The "rmail" program used by UUCP for incoming mail should be
"/usr/sbin/rmail". Likewise, "rsmtp", for receiving batch-SMTP-over-
UUCP, should be "/usr/sbin/rsmtp" if it is supported.

If your package needs to know what hostname to use on (for example)
outgoing news and mail messages which are generated locally, you
should use the file "/etc/mailname". It will contain the portion after
the username and "@" (at) sign for email addresses of users on the
machine (followed by a newline).

Such a package should check for the existence of this file when it is
being configured. If it exists, it should be used without comment,
although an MTA's configuration script may wish to prompt the user
even if it finds that this file exists. If the file does not exist,
the package should prompt the user for the value (preferably using
"debconf") and store it in "/etc/mailname" as well as using it in the
package's configuration. The prompt should make it clear that the name
will not just be used by that package. For example, in this situation
the "inn" package could say something like:

   Please enter the "mail name" of your system.  This is the hostname portion
   of the address to be shown on outgoing news and mail messages.  The
   default is syshostname, your system's host name.

   Mail name ["syshostname"]:

where syshostname is the output of "hostname --fqdn".


11.7. News system configuration
===============================

All the configuration files related to the NNTP (news) servers and
clients should be located under "/etc/news".

There are some configuration issues that apply to a number of news
clients and server packages on the machine. These are:

"/etc/news/organization"
   A string which should appear as the organization header for all
   messages posted by NNTP clients on the machine

"/etc/news/server"
   Contains the FQDN of the upstream NNTP server, or localhost if the
   local machine is an NNTP server.

Other global files may be added as required for cross-package news
configuration.


11.8. Programs for the X Window System
======================================


11.8.1. Providing X support and package priorities
--------------------------------------------------

Programs that can be configured with support for the X Window System
must be configured to do so and must declare any package dependencies
necessary to satisfy their runtime requirements when using the X
Window System. If such a package is of higher priority than the X
packages on which it depends, it is required that either the
X-specific components be split into a separate package, or that an
alternative version of the package, which includes X support, be
provided, or that the package's priority be lowered.


11.8.2. Packages providing an X server
--------------------------------------

Packages that provide an X server that, directly or indirectly,
communicates with real input and display hardware should declare in
their "Provides" control field that they provide the virtual package
"xserver".  [5]


11.8.3. Packages providing a terminal emulator
----------------------------------------------

Packages that provide a terminal emulator for the X Window System
which meet the criteria listed below should declare in their
"Provides" control field that they provide the virtual package "x
-terminal-emulator". They should also register themselves as an
alternative for "/usr/bin/x-terminal-emulator", with a priority of 20.
That alternative should have a slave alternative for
"/usr/share/man/man1/x-terminal-emulator.1.gz" pointing to the
corresponding manual page.

To be an "x-terminal-emulator", a program must:

* Be able to emulate a DEC VT100 terminal, or a compatible terminal.

* Support the command-line option "-e command", which creates a new
  terminal window [6] and runs the specified command.  <command> may
  be multiple arguments, which form the argument list to the executed
  program.  In other words, the behavior is as though the arguments
  were passed directly to "execvp", bypassing the shell. ("xterm"'s
  behavior of falling back on using the shell if "-e" had a single
  argument and exec failed is permissible but not required.)

* Support the command-line option "-T title", which creates a new
  terminal window with the window title title.


11.8.4. Packages providing a window manager
-------------------------------------------

Packages that provide a window manager should declare in their
"Provides" control field that they provide the virtual package "x
-window-manager". They should also register themselves as an
alternative for "/usr/bin/x-window-manager", with a priority
calculated as follows:

* Start with a priority of 40.

* If the window manager complies with The Window Manager Specification
  Project, written by the Free Desktop Group, add 40 points.

* If the window manager permits the X session to be restarted using a
  *different* window manager (without killing the X server) in its
  default configuration, add 10 points; otherwise add none.

That alternative should have a slave alternative for
"/usr/share/man/man1/x-window-manager.1.gz" pointing to the
corresponding manual page.


11.8.5. Packages providing fonts
--------------------------------

Packages that provide fonts for the X Window System  [7] must do a
number of things to ensure that they are both available without
modification of the X or font server configuration, and that they do
not corrupt files used by other font packages to register information
about themselves.

1. Fonts of any type supported by the X Window System must be in a
   separate binary package from any executables, libraries, or
   documentation (except that specific to the fonts shipped, such as
   their license information). If one or more of the fonts so packaged
   are necessary for proper operation of the package with which they
   are associated the font package may be Recommended; if the fonts
   merely provide an enhancement, a Suggests relationship may be used.
   Packages must not Depend on font packages.  [8]

2. BDF fonts must be converted to PCF fonts with the "bdftopcf"
   utility (available in the "xfonts-utils" package, "gzip"ped, and
   placed in a directory that corresponds to their resolution:

   * 100 dpi fonts must be placed in "/usr/share/fonts/X11/100dpi/".

   * 75 dpi fonts must be placed in "/usr/share/fonts/X11/75dpi/".

   * Character-cell fonts, cursor fonts, and other low-resolution
     fonts must be placed in "/usr/share/fonts/X11/misc/".

3. Type 1 fonts must be placed in "/usr/share/fonts/X11/Type1/". If
   font metric files are available, they must be placed here as well.

4. Subdirectories of "/usr/share/fonts/X11/" other than those listed
   above must be neither created nor used. (The "PEX", "CID",
   "Speedo", and "cyrillic" directories are excepted for historical
   reasons, but installation of files into these directories remains
   discouraged.)

5. Font packages may, instead of placing files directly in the X font
   directories listed above, provide symbolic links in that font
   directory pointing to the files' actual location in the filesystem.
   Such a location must comply with the FHS.

6. Font packages should not contain both 75dpi and 100dpi versions of
   a font. If both are available, they should be provided in separate
   binary packages with "-75dpi" or "-100dpi" appended to the names of
   the packages containing the corresponding fonts.

7. Fonts destined for the "misc" subdirectory should not be included
   in the same package as 75dpi or 100dpi fonts; instead, they should
   be provided in a separate package with "-misc" appended to its
   name.

8. Font packages must not provide the files "fonts.dir",
   "fonts.alias", or "fonts.scale" in a font directory:

   * "fonts.dir" files must not be provided at all.

   * "fonts.alias" and "fonts.scale" files, if needed, should be
     provided in the directory
     "/etc/X11/fonts/fontdir/package.extension", where fontdir is the
     name of the subdirectory of "/usr/share/fonts/X11/" where the
     package's corresponding fonts are stored (e.g., "75dpi" or
     "misc"), package is the name of the package that provides these
     fonts, and extension is either "scale" or "alias", whichever
     corresponds to the file contents.

9. Font packages must declare a dependency on "xfonts-utils" in their
   "Depends" or "Pre-Depends" control field.

10. Font packages that provide one or more "fonts.scale" files as
    described above must invoke "update-fonts-scale" on each directory
    into which they installed fonts *before* invoking "update-fonts-
    dir" on that directory. This invocation must occur in both the
    "postinst" (for all arguments) and "postrm" (for all arguments
    except "upgrade") scripts.

11. Font packages that provide one or more "fonts.alias" files as
    described above must invoke "update-fonts-alias" on each directory
    into which they installed fonts. This invocation must occur in
    both the "postinst" (for all arguments) and "postrm" (for all
    arguments except "upgrade") scripts.

12. Font packages must invoke "update-fonts-dir" on each directory
    into which they installed fonts. This invocation must occur in
    both the "postinst" (for all arguments) and "postrm" (for all
    arguments except "upgrade") scripts.

13. Font packages must not provide alias names for the fonts they
    include which collide with alias names already in use by fonts
    already packaged.

14. Font packages must not provide fonts with the same XLFD registry
    name as another font already packaged.


11.8.6. Application defaults files
----------------------------------

Application defaults files must be installed in the directory
"/etc/X11/app-defaults/" (use of a localized subdirectory of
"/etc/X11/" as described in the *X Toolkit Intrinsics - C Language
Interface* manual is also permitted). They must be registered as
"conffile"s or handled as configuration files.

Customization of programs' X resources may also be supported with the
provision of a file with the same name as that of the package placed
in the "/etc/X11/Xresources/" directory, which must be registered as a
"conffile" or handled as a configuration file.  [9]


11.8.7. Installation directory issues
-------------------------------------

Historically, packages using the X Window System used a separate set
of installation directories from other packages. This practice has
been discontinued and packages using the X Window System should now
generally be installed in the same directories as any other package.
Specifically, packages must not install files under the "/usr/X11R6/"
directory and the "/usr/X11R6/" directory hierarchy should be regarded
as obsolete.

Include files previously installed under "/usr/X11R6/include/X11/"
should be installed into "/usr/include/X11/". For files previously
installed into subdirectories of "/usr/X11R6/lib/X11/", package
maintainers should determine if subdirectories of "/usr/lib/" and
"/usr/share/" can be used. If not, a subdirectory of "/usr/lib/X11/"
should be used.

Configuration files for window, display, or session managers or other
applications that are tightly integrated with the X Window System may
be placed in a subdirectory of "/etc/X11/" corresponding to the
package name. Other X Window System applications should use the
"/etc/" directory unless otherwise mandated by policy (such as for
Application defaults files).


11.9. Perl programs and modules
===============================

Perl programs and modules should follow the current Perl policy.

The Perl policy can be found in the "perl-policy" files in the
"debian-policy" package. It is also available from the Debian web
mirrors at https://www.debian.org/doc/packaging-manuals/perl-policy/.


11.10. Emacs lisp programs
==========================

Please refer to the "Debian Emacs Policy" for details of how to
package emacs lisp programs.

The Emacs policy is available in "debian-emacs-policy.gz" of the
emacsen-common package. It is also available from the Debian web
mirrors at https://www.debian.org/doc/packaging-manuals/debian-emacs-
policy.


11.11. Games
============

The permissions on "/var/games" are mode 755, owner "root" and group
"root".

Each game decides on its own security policy.

Games which require protected, privileged access to high-score files,
saved games, etc., may be made set-*group*-id (mode 2755) and owned by
"root:games", and use files and directories with appropriate
permissions (770 "root:games", for example). They must not be made
set-*user*-id, as this causes security problems. (If an attacker can
subvert any set-user-id game they can overwrite the executable of any
other, causing other players of these games to run a Trojan horse
program. With a set-group-id game the attacker only gets access to
less important game data, and if they can get at the other players'
accounts at all it will take considerably more effort.)

Some packages, for example some fortune cookie programs, are
configured by the upstream authors to install with their data files or
other static information made unreadable so that they can only be
accessed through set-id programs provided. You should not do this in a
Debian package: anyone can download the ".deb" file and read the data
from it, so there is no point making the files unreadable. Not making
the files unreadable also means that you don't have to make so many
programs set-id, which reduces the risk of a security hole.

As described in the FHS, binaries of games should be installed in the
directory "/usr/games". This also applies to games that use the X
Window System. Manual pages for games (X and non-X games) should be
installed in "/usr/share/man/man6".

[1] Internally, the package system normalizes the GNU triplets and the
    Debian arches into Debian arch triplets (which are kind of
    inverted GNU triplets), with the first component of the triplet
    representing the libc and ABI in use, and then does matching
    against those triplets. However, such triplets are an internal
    implementation detail that should not be used by packages
    directly. The libc and ABI portion is handled internally by the
    package system based on the os and cpu.

[2] The Debian base system already provides an editor and a pager
    program.

[3] If it is not possible to establish both locks, the system
    shouldn't wait for the second lock to be established, but remove
    the first lock, wait a (random) time, and start over locking
    again.

[4] There are two traditional permission schemes for mail spools: mode
    600 with all mail delivery done by processes running as the
    destination user, or mode 660 and owned by group mail with mail
    delivery done by a process running as a system user in group mail.
    Historically, Debian required mode 660 mail spools to enable the
    latter model, but that model has become increasingly uncommon and
    the principle of least privilege indicates that mail systems that
    use the first model should use permissions of 600. If delivery to
    programs is permitted, it's easier to keep the mail system secure
    if the delivery agent runs as the destination user. Debian Policy
    therefore permits either scheme.

[5] This implements current practice, and provides an actual policy
    for usage of the "xserver" virtual package which appears in the
    virtual packages list. In a nutshell, X servers that interface
    directly with the display and input hardware or via another
    subsystem (e.g., GGI) should provide "xserver". Things like
    "Xvfb", "Xnest", and "Xprt" should not.

[6] "New terminal window" does not necessarily mean a new top-level X
    window directly parented by the window manager; it could, if the
    terminal emulator application were so coded, be a new "view" in a
    multiple-document interface (MDI).

[7] For the purposes of Debian Policy, a "font for the X Window
    System" is one which is accessed via X protocol requests. Fonts
    for the Linux console, for PostScript renderer, or any other
    purpose, do not fit this definition. Any tool which makes such
    fonts available to the X Window System, however, must abide by
    this font policy.

[8] This is because an X client may be displayed by a remote X server,
    in which case X fonts are provided by the remote X server, not
    retrieved locally; the Debian package system is empowered to deal
    only with the local file system.

[9] Note that this mechanism is not the same as using app-defaults;
    app-defaults are tied to the client binary on the local file
    system, whereas X resources are stored in the X server and affect
    all connecting clients.



12. Documentation
*****************


12.1. Manual pages
==================

You should install manual pages in "nroff" source form, in appropriate
places under "/usr/share/man". You should only use sections 1 to 9
(see the FHS for more details). You must not install a pre-formatted
"cat page".

Each program, utility, and function should have an associated manual
page included in the same package or a dependency. It is suggested
that all configuration files also have a manual page included as well.
Manual pages for protocols and other auxiliary things are optional.

If no manual page is available, this is considered as a bug and should
be reported to the Debian Bug Tracking System (the maintainer of the
package is allowed to write this bug report themselves, if they so
desire). Do not close the bug report until a proper man page is
available.  [1]

You may forward a complaint about a missing man page to the upstream
authors, and mark the bug as forwarded in the Debian bug tracking
system. Even though the GNU Project do not in general consider the
lack of a man page to be a bug, we do; if they tell you that they
don't consider it a bug you should leave the bug in our bug tracking
system open anyway.

Manual pages should be installed compressed using "gzip -9".

If one man page needs to be accessible via several names it is better
to use a symbolic link than the ".so" feature, but there is no need to
fiddle with the relevant parts of the upstream source to change from
".so" to symlinks: don't do it unless it's easy. You should not create
hard links in the manual page directories, nor put absolute filenames
in ".so" directives. The filename in a ".so" in a man page should be
relative to the base of the man page tree (usually "/usr/share/man").
If you do not create any links (whether symlinks, hard links, or ".so"
directives) in the file system to the alternate names of the man page,
then you should not rely on "man" finding your man page under those
names based solely on the information in the man page's header.  [2]

Manual pages in locale-specific subdirectories of "/usr/share/man"
should use either UTF-8 or the usual legacy encoding for that language
(normally the one corresponding to the shortest relevant locale name
in "/usr/share/i18n/SUPPORTED"). For example, pages under
"/usr/share/man/fr" should use either UTF-8 or ISO-8859-1.  [3]

A country name (the "DE" in "de_DE") should not be included in the
subdirectory name unless it indicates a significant difference in the
language, as this excludes speakers of the language in other
countries. [4]

If a localized version of a manual page is provided, it should either
be up-to-date or it should be obvious to the reader that it is
outdated and the original manual page should be used instead. This can
be done either by a note at the beginning of the manual page or by
showing the missing or changed portions in the original language
instead of the target language.

Packages (other than manual page readers) must not require the
existence of any files in "/usr/share/man/" in order to function. A
package that optionally displays its own manual pages, such as to
provide user help, must fail gracefully if the manual pages aren't
installed.


12.2. Info documents
====================

Info documents should be installed in "/usr/share/info". They should
be compressed with "gzip -9".

The "install-info" program maintains a directory of installed info
documents in "/usr/share/info/dir" for the use of info readers. This
file must not be included in packages other than install-info.

"install-info" is automatically invoked when appropriate using dpkg
triggers. Packages other than install-info *should not* invoke
"install-info" directly and *should not* depend on, recommend, or
suggest install-info for this purpose.

Info readers requiring the "/usr/share/info/dir" file should depend on
install-info.

Info documents should contain section and directory entry information
in the document for the use of "install-info". The section should be
specified via a line starting with "INFO-DIR-SECTION" followed by a
space and the section of this info page. The directory entry or
entries should be included between a "START-INFO-DIR-ENTRY" line and
an "END-INFO-DIR-ENTRY" line. For example:

   INFO-DIR-SECTION Individual utilities
   START-INFO-DIR-ENTRY
   * example: (example).               An example info directory entry.
   END-INFO-DIR-ENTRY

To determine which section to use, you should look at
"/usr/share/info/dir" on your system and choose the most relevant (or
create a new section if none of the current sections are relevant).
[5]

Packages (other than info readers) must not require the existence of
any files in "/usr/share/info/" in order to function.


12.3. Additional documentation
==============================

Any additional documentation that comes with the package may be
installed at the discretion of the package maintainer. It is often a
good idea to include text information files ("README"s, FAQs, and so
forth) that come with the source package in the binary package.
However, you don't need to install the instructions for building and
installing the package, of course!

Plain text documentation should be compressed with "gzip -9" unless it
is small.

If a package comes with large amounts of documentation that many users
of the package will not require, you should create a separate binary
package to contain it so that it does not take up disk space on the
machines of users who do not need or want it installed. As a special
case of this rule, shared library documentation of any appreciable
size should always be packaged with the library development package
(Development files) or in a separate documentation package, since
shared libraries are frequently installed as dependencies of other
packages by users who have little interest in documentation of the
library itself. The documentation package for the package package is
conventionally named package-doc (or package-doc-language-code if
there are separate documentation packages for multiple languages).

If package is a build tool, development tool, command-line tool, or
library development package, package (or package-dev in the case of a
library development package) already provides documentation in man,
info, or plain text format, and package-doc provides HTML or other
formats, package should declare at most a "Suggests" on package-doc.
Otherwise, package should declare at most a "Recommends" on package-
doc.

Additional documentation included in the package should be installed
under "/usr/share/doc/package". If the documentation is packaged
separately, as package-doc for example, it may be installed under
either that path or into the documentation directory for the separate
documentation package ("/usr/share/doc/package-doc" in this example).
However, installing the documentation into the documentation directory
of the main package is encouraged since it is independent of the
packaging method and will be easier for users to find.

Any separate package providing documentation must still install
standard documentation files in its own "/usr/share/doc" directory as
specified in the rest of this policy. See, for example, Copyright
information and Changelog files and release notes.

Packages must not require the existence of any files in
"/usr/share/doc/" in order to function.  [6] Any files that are used
or read by programs but are also useful as stand alone documentation
should be installed elsewhere, such as under "/usr/share/package/",
and then included via symbolic links in "/usr/share/doc/package".

"/usr/share/doc/package" is permitted to be a symbolic link to another
directory in "/usr/share/doc" only if the two packages both come from
the same source and the first package Depends on the second.
Otherwise, "/usr/share/doc/package" must not be a symbolic link. [7]


12.4. Preferred documentation formats
=====================================

The unification of Debian documentation is being carried out via HTML.

If the package comes with extensive documentation in a markup format
that can be converted to various other formats you should if possible
ship HTML versions in a binary package.  [8] The documentation must be
installed as specified in Additional documentation.

Other formats such as PostScript may be provided at the package
maintainer's discretion.


12.5. Copyright information
===========================

Every package must be accompanied by a verbatim copy of its
distribution license(s) in the file
"/usr/share/doc/PACKAGE/copyright". This file must neither be
compressed nor be a symbolic link.

A verbatim copy of the package's copyright information is often
required to be present in "/usr/share/doc/PACKAGE/copyright", too; see
Copyright considerations.

In addition, the copyright file must say where the upstream sources
(if any) were obtained, and should include a name or contact address
for the upstream authors. This can be the name of an individual or an
organization, an email address, a web forum or bugtracker, or any
other means to unambiguously identify who to contact to participate in
the development of the upstream source code.

Packages in the *contrib*, *non-free*, or *non-free-firmware* archive
areas should state in the copyright file that the package is not part
of the Debian distribution and briefly explain why.

A copy of the file which will be installed in
"/usr/share/doc/PACKAGE/copyright" should be in "debian/copyright" in
the source package.

"/usr/share/doc/package" is permitted be a symbolic link to another
directory in "/usr/share/doc" only if the two packages both come from
the same source and the first package Depends on the second.
Otherwise, "/usr/share/doc/package" must not be a symbolic link. These
rules are important because "copyright" files must be extractable by
mechanical means.

Packages distributed under the Apache license (version 2.0), the
Artistic license, the Creative Commons CC0-1.0 license, the GNU GPL
(versions 1, 2, or 3), the GNU LGPL (versions 2, 2.1, or 3), the GNU
FDL (versions 1.2 or 1.3), and the Mozilla Public License (version 1.1
or 2.0) should refer to the corresponding files under "/usr/share
/common-licenses",  [9] rather than quoting them in the copyright
file.

You should not use the copyright file as a general "README" file. If
your package has such a file it should be installed in
"/usr/share/doc/package/README" or "README.Debian" or some other
appropriate place.

All copyright files must be encoded in UTF-8.


12.5.1. Machine-readable copyright information
----------------------------------------------

A specification for a standard, machine-readable format for
"debian/copyright" files is maintained as part of the debian-policy
package. This document is in the "copyright-format" files in the
debian-policy package. It is also available from the Debian web
mirrors at https://www.debian.org/doc/packaging-manuals/copyright-
format/1.0/.

Use of this format is optional.


12.6. Examples
==============

Any examples (configurations, source files, whatever), should be
installed in a directory "/usr/share/doc/package/examples". These
files should not be referenced by any program: they're there for the
benefit of the system administrator and users as documentation only.
Architecture-specific example files should be installed in a directory
"/usr/lib/package/examples" with symbolic links to them from
"/usr/share/doc/package/examples", or the latter directory itself may
be a symbolic link to the former.

If the purpose of a package is to provide examples, then the example
files may be installed into "/usr/share/doc/package".


12.7. Changelog files and release notes
=======================================

Packages that are not Debian-native must contain a compressed copy of
the "debian/changelog" file from the Debian source tree in
"/usr/share/doc/package" with the name "changelog.Debian.gz".

If an upstream release notes file is available, containing a summary
of changes between upstream releases intended for end users of the
package and often called "NEWS", it should be accessible as
"/usr/share/doc/package/NEWS.gz".  An older practice of installing the
upstream release notes as "/usr/share/doc/package/changelog.gz" is
permitted but deprecated.

If there is an upstream changelog available, it may be made available
as "/usr/share/doc/package/changelog.gz".

If either of these files are distributed in HTML, they should be made
available at "/usr/share/doc/package/NEWS.html.gz" and
"/usr/share/doc/package/changelog.html.gz" respectively, and plain
text versions "NEWS.gz" and "changelog.gz" should be generated from
them, using, for example, "lynx -dump -nolist".

If the upstream release notes or changelog do not already conform to
this naming convention, then this may be achieved either by renaming
the files, or by adding a symbolic link, at the maintainer's
discretion.  [10]

All of these files should be installed compressed using "gzip -9", as
they will become large with time even if they start out small.

If the package has only one file which is used both as the Debian
changelog and the upstream release notes or changelog, because there
is no separate upstream maintainer, then that file should usually be
installed as "/usr/share/doc/package/NEWS.gz" or
"/usr/share/doc/package/changelog.gz" (depending on whether the file
is release notes or a changelog); if there is a separate upstream
maintainer, but no upstream release notes or changelog, then the
Debian changelog should still be called "changelog.Debian.gz".

For details about the format and contents of the Debian changelog
file, please see Debian changelog: debian/changelog.

[1] It is not very hard to write a man page. See the Man-Page-HOWTO,
    *man(7)*, the examples created by "dh_make", the helper program
    "help2man", or the directory "/usr/share/doc/man-db/examples".

[2] Supporting this in "man" often requires unreasonable processing
    time to find a manual page or to report that none exists, and
    moves knowledge into man's database that would be better left in
    the file system. This support is therefore deprecated and will
    cease to be present in the future.

[3] "man" will automatically detect whether UTF-8 is in use. In
    future, all manual pages will be required to use UTF-8.

[4] At the time of writing, Chinese and Portuguese are the main
    languages with such differences, so "pt_BR", "zh_CN", and "zh_TW"
    are all allowed.

[5] Normally, info documents are generated from Texinfo source. To
    include this information in the generated info document, if it is
    absent, add commands like:

       @dircategory Individual utilities
       @direntry
       * example: (example).  An example info directory entry.
       @end direntry

    to the Texinfo source of the document and ensure that the info
    documents are rebuilt from source during the package build.

[6] The system administrator should be able to delete files in
    "/usr/share/doc/" without causing any programs to break.

[7] Please note that this does not override the section on changelog
    files below, so the file
    "/usr/share/doc/package/changelog.Debian.gz" must refer to the
    changelog for the current version of package in question. In
    practice, this means that the sources of the target and the
    destination of the symlink must be the same (same source package
    and version).

[8] Rationale: The important thing here is that HTML documentation
    should be available from *some* binary package.

[9] In particular, "/usr/share/common-licenses/Apache-2.0",
    "/usr/share/common-licenses/Artistic", "/usr/share/common-
    licenses/CC0-1.0", "/usr/share/common-licenses/GPL-1", "/usr/share
    /common-licenses/GPL-2", "/usr/share/common-licenses/GPL-3",
    "/usr/share/common-licenses/LGPL-2", "/usr/share/common-
    licenses/LGPL-2.1", "/usr/share/common-licenses/LGPL-3",
    "/usr/share/common-licenses/GFDL-1.2", "/usr/share/common-
    licenses/GFDL-1.3", "/usr/share/common-licenses/MPL-1.1", and
    "/usr/share/common-licenses/MPL-2.0" respectively. The University
    of California BSD license used to be included in base-files as
    "/usr/share/common-licenses/BSD", but given the brevity of this
    license, its specificity to code whose copyright is held by the
    Regents of the University of California, and the frequency of
    minor wording changes, its text must be included in the copyright
    file.

[10] Rationale: People should not have to look in places for upstream
     changelogs merely because they are given different names or are
     distributed in HTML format.



1. Introduction and scope of these appendices
*********************************************

These appendices, except the final three, are taken essentially
verbatim from the now-deprecated Packaging Manual, version 3.2.1.0.
They are the chapters which are likely to be of use to package
maintainers and which have not already been included in the policy
document itself. Most of these sections are very likely not relevant
to policy; they should be treated as documentation for the packaging
system. Please note that these appendices are included for
convenience, and for historical reasons: they used to be part of
policy package, and they have not yet been incorporated into dpkg
documentation. However, they still have value, and hence they are
presented here.

They have not yet been checked to ensure that they are compatible with
the contents of policy, and if there are any contradictions, the
version in the main policy document takes precedence. The remaining
chapters of the old Packaging Manual have also not been read in detail
to ensure that there are not parts which have been left out. Both of
these will be done in due course.

Certain parts of the Packaging manual were integrated into the Policy
Manual proper, and removed from the appendices. Links have been placed
from the old locations to the new ones.

"dpkg" is a suite of programs for creating binary package files and
installing and removing them on Unix systems.  [1]

The binary packages are designed for the management of installed
executable programs (usually compiled binaries) and their associated
data, though source code examples and documentation are provided as
part of some packages.

This manual describes the technical aspects of creating Debian binary
packages (".deb" files). It documents the behavior of the package
management programs "dpkg", "dselect" et al. and the way they interact
with packages.

This manual does not go into detail about the options and usage of the
package building and installation tools. It should therefore be read
in conjunction with those programs' man pages.

The utility programs which are provided with "dpkg" not described in
detail here, are documented in their man pages.

It is assumed that the reader is reasonably familiar with the "dpkg"
System Administrators' manual. Unfortunately this manual does not yet
exist.

The Debian version of the FSF's GNU hello program is provided as an
example for people wishing to create Debian packages. However, while
the examples are helpful, they do not replace the need to read and
follow the Policy and Programmer's Manual.

[1] "dpkg" is targeted primarily at Debian, but may work on or be
    ported to other systems.



2. Binary packages (from old Packaging Manual)
**********************************************

See *deb(5)* and Binary package metadata files.


2.1. Creating package files - "dpkg-deb"
========================================

All manipulation of binary package files is done by "dpkg-deb"; it's
the only program that has knowledge of the format. ("dpkg-deb" may be
invoked by calling "dpkg", as "dpkg" will spot that the options
requested are appropriate to "dpkg-deb" and invoke that instead with
the same arguments.)

In order to create a binary package, you must make a directory tree
which contains all the files and directories you want to have in the
file system data part of the package. In Debian-format source
packages, this directory is usually either "debian/tmp" or
"debian/pkg", relative to the top of the package's source tree.

They should have the locations (relative to the root of the directory
tree you're constructing) ownerships and permissions which you want
them to have on the system when they are installed.

With current versions of "dpkg" the uid/username and gid/groupname
mappings for the users and groups being used should be the same on the
system where the package is built and the one where it is installed.

You need to add one special directory to the root of the miniature
file system tree you're creating: "DEBIAN". It should contain the
control information files, notably the binary package control file
(see The binary package control file: control).

The "DEBIAN" directory will not appear in the file system archive of
the package, and so won't be installed by "dpkg" when the package is
unpacked.

When you've prepared the package, you should invoke:

   dpkg --build directory

This will build the package in "directory.deb". ("dpkg" knows that "--
build" is a "dpkg-deb" option, so it invokes "dpkg-deb" with the same
arguments to build the package.)

See the *dpkg-deb(8)* man page for details of how to examine the
contents of this newly-created file. You may find the output of
following commands enlightening:

   dpkg-deb --info filename.deb
   dpkg-deb --contents filename.deb
   dpkg --contents filename.deb

To view the copyright file for a package you could use this command:

   dpkg --fsys-tarfile filename.deb | tar xOf - --wildcards \*/copyright | pager


2.2. Binary package metadata files
==================================

The package metadata portion of a binary package is a collection of
files with names known to "dpkg". It will treat the contents of these
files specially - some of them contain information used by "dpkg" when
installing or removing the package; others are scripts which the
package maintainer wants "dpkg" to run.

It is possible to put other files in the package metadata archive
member, but this is not generally a good idea (though they will
largely be ignored).

Here is a brief list of the package metadata files supported by "dpkg"
and a summary of what they're used for.

"control"
   This is the key description file used by "dpkg". It specifies the
   package's name and version, gives its description for the user,
   states its relationships with other packages, and so forth. See
   Debian source package template control files -- debian/control and
   Debian binary package control files -- DEBIAN/control.

   It is usually generated automatically from information in the
   source package by the "dpkg-gencontrol" program, and with
   assistance from "dpkg-shlibdeps". See Source packages (from old
   Packaging Manual).

"postinst", "preinst", "postrm", "prerm"
   These are executable files (usually scripts) which "dpkg" runs
   during installation, upgrade and removal of packages. They allow
   the package to deal with matters which are particular to that
   package or require more complicated processing than that provided
   by "dpkg". Details of when and how they are called are in Package
   maintainer scripts and installation procedure.

   It is very important to make these scripts idempotent. See
   Maintainer scripts idempotency.

   The maintainer scripts are not guaranteed to run with a controlling
   terminal and may not be able to interact with the user. See
   Controlling terminal for maintainer scripts.

"conffiles" This file contains a list of configuration files which
   are to be handled automatically by "dpkg" (see Configuration file
   handling (from old Packaging Manual)). Note that not necessarily
   every configuration file should be listed here.

"shlibs"
   This file contains a list of the shared libraries supplied by the
   package, with dependency details for each. This is used by "dpkg-
   shlibdeps" when it determines what dependencies are required in a
   package control file. The "shlibs" file format is described on The
   shlibs File Format.


2.3. The binary package control file: "control"
===============================================

The most important package metadata file used by "dpkg" when it
installs a package is "control". It contains all the package's "vital
statistics".

The binary package control files of packages built from Debian sources
are made by a special tool, "dpkg-gencontrol", which reads
"debian/control" and "debian/changelog" to find the information it
needs. See Source packages (from old Packaging Manual) for more
details.

The fields in binary package control files are listed in Debian binary
package control files -- DEBIAN/control.

A description of the syntax of control files and the purpose of the
fields is available in Control files and their fields.


2.4. Time Stamps
================

See Time Stamps.



3. Source packages (from old Packaging Manual)
**********************************************

The Debian binary packages in the distribution are generated from
Debian sources, which are in a special format to assist the easy and
automatic building of binaries.


3.1. Tools for processing source packages
=========================================

Various tools are provided for manipulating source packages; they pack
and unpack sources and help build of binary packages and help manage
the distribution of new versions.

They are introduced and typical uses described here; see *dpkg-
source(1)* for full documentation about their arguments and operation.

For examples of how to construct a Debian source package, and how to
use those utilities that are used by Debian source packages, please
see the "hello" example package.


3.1.1. "dpkg-source" - packs and unpacks Debian source packages
---------------------------------------------------------------

This program is frequently used by hand, and is also called from
package-independent automated building scripts such as "dpkg-
buildpackage".

To unpack a package it is typically invoked with

   dpkg-source -x .../path/to/filename.dsc

with the "filename.tar.gz" and "filename.diff.gz" (if applicable) in
the same directory. It unpacks into "package-version", and if
applicable "package-version.orig", in the current directory.

To create a packed source archive it is typically invoked:

   dpkg-source -b package-version

This will create the ".dsc", ".tar.gz" and ".diff.gz" (if appropriate)
in the current directory. "dpkg-source" does not clean the source tree
first - this must be done separately if it is required.

See also Source packages as archives.


3.1.2. "dpkg-buildpackage" - overall package-building control script
--------------------------------------------------------------------

See *dpkg-buildpackage(1)*.


3.1.3. "dpkg-gencontrol" - generates binary package control files
-----------------------------------------------------------------

This program is usually called from "debian/rules" (see section_title)
in the top level of the source tree.

This is usually done just before the files and directories in the
temporary directory tree where the package is being built have their
permissions and ownerships set and the package is constructed using
"dpkg-deb/".  [1]

"dpkg-gencontrol" must be called after all the files which are to go
into the package have been placed in the temporary build directory, so
that its calculation of the installed size of a package is correct.

It is also necessary for "dpkg-gencontrol" to be run after "dpkg-
shlibdeps" so that the variable substitutions created by "dpkg-
shlibdeps" in "debian/substvars" are available.

For a package which generates only one binary package, and which
builds it in "debian/tmp" relative to the top of the source package,
it is usually sufficient to call "dpkg-gencontrol".

Sources which build several binaries will typically need something
like:

   dpkg-gencontrol -Pdebian/pkg -ppackage

The "-P" tells "dpkg-gencontrol" that the package is being built in a
non-default directory, and the "-p" tells it which binary package's
control file should be generated.

"dpkg-gencontrol" also adds information to the list of files in
"debian/files", for the benefit of (for example) a future invocation
of "dpkg-genchanges".


3.1.4. "dpkg-shlibdeps" - calculates shared library dependencies
----------------------------------------------------------------

See *dpkg-shlibdeps(1)*.


3.1.5. "dpkg-distaddfile" - adds a file to "debian/files"
---------------------------------------------------------

Some packages' uploads need to include files other than the source and
binary package files.

"dpkg-distaddfile" adds a file to the "debian/files" file so that it
will be included in the ".changes" file when "dpkg-genchanges" is run.

It is usually invoked from the "binary" target of "debian/rules":

   dpkg-distaddfile filename section priority

The filename is relative to the directory where "dpkg-genchanges" will
expect to find it - this is usually the directory above the top level
of the source tree. The "debian/rules" target should put the file
there just before or just after calling "dpkg-distaddfile".

The section and priority are passed unchanged into the resulting
".changes" file.


3.1.6. "dpkg-genchanges" - generates a ".changes" upload control file
---------------------------------------------------------------------

See *dpkg-genchanges(1)*.


3.1.7. "dpkg-parsechangelog" - produces parsed representation of a changelog
----------------------------------------------------------------------------

See *dpkg-parsechangelog(1)*.


3.1.8. "dpkg-architecture" - information about the build and host system
------------------------------------------------------------------------

See *dpkg-architecture(1)*.


3.2. The Debian package source tree
===================================

The source archive scheme described later is intended to allow a
Debian package source tree with some associated package metadata to be
reproduced and transported easily. The Debian package source tree is a
version of the original program with certain files added for the
benefit of the packaging process, and with any other changes required
made to the rest of the source code and installation scripts.

The extra files created for Debian are in the subdirectory "debian" of
the top level of the Debian package source tree. They are described
below.


3.2.1. "debian/rules" - the main building script
------------------------------------------------

See Main building script: debian/rules.


3.2.2. "debian/substvars" and variable substitutions
----------------------------------------------------

See Variable substitutions: debian/substvars.


3.2.3. "debian/files"
---------------------

See Generated files list: debian/files.


3.2.4. "debian/tmp"
-------------------

This is the default temporary location for the construction of binary
packages by the "binary" target. The directory "tmp" serves as the
root of the file system tree as it is being constructed (for example,
by using the package's upstream makefiles install targets and
redirecting the output there), and it also contains the "DEBIAN"
subdirectory. See Creating package files - dpkg-deb.

This is only a default and can be easily overridden. Most packaging
tools no longer use "debian/tmp", instead preferring "debian/pkg" for
the common case of a source package building only one binary package.
Such tools usually only use "debian/tmp" as a temporary staging area
for built files and do not construct packages from it.

If several binary packages are generated from the same source tree, it
is usual to use a separate "debian/pkg" directory for each binary
package as the temporary construction locations.

Whatever temporary directories are created and used by the "binary"
target must of course be removed by the "clean" target.


3.3. Source packages as archives
================================

As it exists on the FTP site, a Debian source package consists of
three related files. You must have the right versions of all three to
be able to use them.

Debian source control file - ".dsc"
   This file is a control file used by "dpkg-source" to extract a
   source package. See Debian source package control files -- .dsc.

Original source archive - "package_upstream-version.orig.tar.gz"
   This is a compressed (with "gzip -9") "tar" file containing the
   source code from the upstream authors of the program.

Debian package diff - "package_upstream_version-revision.diff.gz"
   This is a unified context diff ("diff -u") giving the changes which
   are required to turn the original source into the Debian source.
   These changes may only include editing and creating plain files.
   The permissions of files, the targets of symbolic links and the
   characteristics of special files or pipes may not be changed and no
   files may be removed or renamed.

   All the directories in the diff must exist, except the "debian"
   subdirectory of the top of the source tree, which will be created
   by "dpkg-source" if necessary when unpacking.

   The "dpkg-source" program will automatically make the
   "debian/rules" file executable (see below).

If there is no original source code - for example, if the package is
specially prepared for Debian or the Debian maintainer is the same as
the upstream maintainer - the format is slightly different: then there
is no diff, and the tarfile is named "package_version.tar.gz", and
preferably contains a directory named "package-version".


3.4. Unpacking a Debian source package without "dpkg-source"
============================================================

"dpkg-source -x" is the recommended way to unpack a Debian source
package. However, if it is not available it is possible to unpack a
Debian source archive as follows:

1. Untar the tarfile, which will create a ".orig" directory.

2. Rename the ".orig" directory to "package-version".

3. Create the subdirectory "debian" at the top of the source tree.

4. Apply the diff using "patch -p0".

5. Untar the tarfile again if you want a copy of the original source
   code alongside the Debian version.

It is not possible to generate a valid Debian source archive without
using "dpkg-source". In particular, attempting to use "diff" directly
to generate the ".diff.gz" file will not work.


3.4.1. Restrictions on objects in source packages
-------------------------------------------------

The source package may not contain any hard links, [2] [3] device
special files, sockets or setuid or setgid files.  [4]

The source packaging tools manage the changes between the original and
Debian source using "diff" and "patch". Turning the original source
tree as included in the ".orig.tar.gz" into the Debian package source
must not involve any changes which cannot be handled by these tools.
Problematic changes which cause "dpkg-source" to halt with an error
when building the source package are:

* Adding or removing symbolic links, sockets or pipes.

* Changing the targets of symbolic links.

* Creating directories, other than "debian".

* Changes to the contents of binary files.

Changes which cause "dpkg-source" to print a warning but continue
anyway are:

* Removing files, directories or symlinks.  [5]

* Changed text files which are missing the usual final newline (either
  in the original or the modified source tree).

Changes which are not represented, but which are not detected by
"dpkg-source", are:

* Changing the permissions of files (other than "debian/rules") and
  directories.

The "debian" directory and "debian/rules" are handled specially by
"dpkg-source" - before applying the changes it will create the
"debian" directory, and afterwards it will make "debian/rules" world-
executable.

[1] This is so that the control file which is produced has the right
    permissions

[2] This is not currently detected when building source packages, but
    only when extracting them.

[3] Hard links may be permitted at some point in the future, but would
    require a fair amount of work.

[4] Setgid directories are allowed.

[5] Renaming a file is not treated specially - it is seen as the
    removal of the old file (which generates a warning, but is
    otherwise ignored), and the creation of the new one.



4. Control files and their fields (from old Packaging Manual)
*************************************************************

Many of the tools in the "dpkg" suite manipulate data in a common
format, known as control files. Binary and source packages have
control data as do the ".changes" files which control the installation
of uploaded files, and "dpkg"'s internal databases are in a similar
format.


4.1. Syntax of control files
============================

See Syntax of control files.

It is important to note that there are several fields which are
optional as far as "dpkg" and the related tools are concerned, but
which must appear in every Debian package, or whose omission may cause
problems.


4.2. List of fields
===================

See List of fields.

This section now contains only the fields that didn't belong to the
Policy manual.


4.2.1. "Filename"
-----------------

This field in "Packages" files give the filename(s) of (the parts of)
a package in the distribution directories, relative to the root of the
Debian hierarchy. If the package has been split into several parts the
parts are all listed in order, separated by spaces.


4.2.2. "Size" and "MD5sum"
--------------------------

These fields in "Packages" files give the size (in bytes, expressed in
decimal) and MD5 checksum of the file(s) which make(s) up a binary
package in the distribution. If the package is split into several
parts the values for the parts are listed in order, separated by
spaces.


4.2.3. "Status"
---------------

This field in "dpkg"'s status file records whether the user wants a
package installed, removed or left alone, whether it is broken
(requiring re-installation) or not and what its current state on the
system is. Each of these pieces of information is a single word.


4.2.4. "Config-Version"
-----------------------

If a package is not installed or not configured, this field in
"dpkg"'s status file records the last version of the package which was
successfully configured.


4.2.5. "Conffiles"
------------------

This field in "dpkg"'s status file contains information about the
automatically-managed configuration files held by a package. This
field should *not* appear anywhere in a package!


4.2.6. Obsolete fields
----------------------

These are still recognized by "dpkg" but should not appear anywhere
any more.

"Revision"; "Package-Revision"; "Package_Revision"
   The Debian revision part of the package version was at one point in
   a separate control field. This field went through several names.

"Recommended"
   Old name for "Recommends".

"Optional"
   Old name for "Suggests".

"Class"
   Old name for "Priority".



5. Configuration file handling (from old Packaging Manual)
**********************************************************

"dpkg" can do a certain amount of automatic handling of package
configuration files.

Whether this mechanism is appropriate depends on a number of factors,
but basically there are two approaches to any particular configuration
file.

The easy method is to ship a best-effort configuration in the package,
and use "dpkg"'s conffile mechanism to handle updates. If the user is
unlikely to want to edit the file, but you need them to be able to
without losing their changes, and a new package with a changed version
of the file is only released infrequently, this is a good approach.

The hard method is to build the configuration file from scratch in the
"postinst" script, and to take the responsibility for fixing any
mistakes made in earlier versions of the package automatically. This
will be appropriate if the file is likely to need to be different on
each system.


5.1. Automatic handling of configuration files by "dpkg"
========================================================

A binary package may contain a package metadata file called
"conffiles". This file should be a list of filenames of configuration
files needing automatic handling, separated by newlines. The filenames
should be absolute pathnames, and the files referred to should
actually exist in the package.

When a package is upgraded "dpkg" will process the configuration files
during the configuration stage, shortly before it runs the package's
"postinst" script,

For each file it checks to see whether the version of the file
included in the package is the same as the one that was included in
the last version of the package (the one that is being upgraded from);
it also compares the version currently installed on the system with
the one shipped with the last version.

If neither the user nor the package maintainer has changed the file,
it is left alone. If one or the other has changed their version, then
the changed version is preferred - i.e., if the user edits their file,
but the package maintainer doesn't ship a different version, the
user's changes will stay, silently, but if the maintainer ships a new
version and the user hasn't edited it the new version will be
installed (with an informative message). If both have changed their
version the user is prompted about the problem and must resolve the
differences themselves.

The comparisons are done by calculating the MD5 message digests of the
files, and storing the MD5 of the file as it was included in the most
recent version of the package.

When a package is installed for the first time "dpkg" will install the
file that comes with it, unless that would mean overwriting a file
already on the file system.

However, note that "dpkg" will *not* replace a conffile that was
removed by the user (or by a script). This is necessary because with
some programs a missing file produces an effect hard or impossible to
achieve in another way, so that a missing file needs to be kept that
way if the user did it.

Note that a package should *not* modify a "dpkg"-handled conffile in
its maintainer scripts. Doing this will lead to "dpkg" giving the user
confusing and possibly dangerous options for conffile update when the
package is upgraded.


5.2. Fully-featured maintainer script configuration handling
============================================================

For files which contain site-specific information such as the hostname
and networking details and so forth, it is better to create the file
in the package's "postinst" script.

This will typically involve examining the state of the rest of the
system to determine values and other information, and may involve
prompting the user for some information which can't be obtained some
other way.

When using this method there are a couple of important issues which
should be considered:

If you discover a bug in the program which generates the configuration
file, or if the format of the file changes from one version to the
next, you will have to arrange for the postinst script to do something
sensible - usually this will mean editing the installed configuration
file to remove the problem or change the syntax. You will have to do
this very carefully, since the user may have changed the file, perhaps
to fix the very problem that your script is trying to deal with - you
will have to detect these situations and deal with them correctly.

If you do go down this route it's probably a good idea to make the
program that generates the configuration file(s) a separate program in
"/usr/sbin", by convention called "packageconfig" and then run that if
appropriate from the post-installation script. The "packageconfig"
program should not unquestioningly overwrite an existing configuration
- if its mode of operation is geared towards setting up a package for
the first time (rather than any arbitrary reconfiguration later) you
should have it check whether the configuration already exists, and
require a "--force" flag to overwrite it.



6. Alternative versions of an interface - "update-alternatives" (from old Packaging Manual)
*******************************************************************************************

When several packages all provide different versions of the same
program or file it is useful to have the system select a default, but
to allow the system administrator to change it and have their
decisions respected.

For example, there are several versions of the "vi" editor, and there
is no reason to prevent all of them from being installed at once, each
under their own name ("nvi", "vim" or whatever). Nevertheless it is
desirable to have the name "vi" refer to something, at least by
default.

If all the packages involved cooperate, this can be done with "update-
alternatives".

Each package provides its own version under its own name, and calls
"update-alternatives" in its postinst to register its version (and
again in its prerm to deregister it).

See the *update-alternatives(8)* man page for details.

If "update-alternatives" does not seem appropriate you may wish to
consider using diversions instead.

Do not use alternatives for "systemd" configuration files. See Binary
packages for more information.



7. Diversions - overriding a package's version of a file (from old Packaging Manual)
************************************************************************************

It is possible to have "dpkg" not overwrite a file when it reinstalls
the package it belongs to, and to have it put the file from the
package somewhere else instead.

This can be used locally to override a package's version of a file, or
by one package to override another's version (or provide a wrapper for
it).

Before deciding to use a diversion, read Alternative versions of an
interface - update-alternatives (from old Packaging Manual) to see if
you really want a diversion rather than several alternative versions
of a program.

There is a diversion list, which is read by "dpkg", and updated by a
special program "dpkg-divert". Please see *dpkg-divert(8)* for full
details of its operation.

When a package wishes to divert a file from another, it should call
"dpkg-divert" in its preinst to add the diversion and rename the
existing file. For example, supposing that a "smailwrapper" package
wishes to install a wrapper around "/usr/sbin/smail":

   dpkg-divert --package smailwrapper --add --rename \
       --divert /usr/sbin/smail.real /usr/sbin/smail

The "--package smailwrapper" ensures that "smailwrapper"'s copy of
"/usr/sbin/smail" can bypass the diversion and get installed as the
true version. It's safe to add the diversion unconditionally on
upgrades since it will be left unchanged if it already exists, but
"dpkg-divert" will display a message. To suppress that message, make
the command conditional on the version from which the package is being
upgraded:

   if [ upgrade != "$1" ] || dpkg --compare-versions "$2" lt 1.0-2; then
       dpkg-divert --package smailwrapper --add --rename \
           --divert /usr/sbin/smail.real /usr/sbin/smail
   fi

where "1.0-2" is the version at which the diversion was first added to
the package. Running the command during abort-upgrade is pointless but
harmless.

The postrm has to do the reverse:

   if [ remove = "$1" -o abort-install = "$1" -o disappear = "$1" ]; then
       dpkg-divert --package smailwrapper --remove --rename \
           --divert /usr/sbin/smail.real /usr/sbin/smail
   fi

If the diversion was added at a particular version, the postrm should
also handle the failure case of upgrading from an older version
(unless the older version is so old that direct upgrades are no longer
supported):

   if [ abort-upgrade = "$1" ] && dpkg --compare-versions "$2" lt 1.0-2; then
       dpkg-divert --package smailwrapper --remove --rename \
           --divert /usr/sbin/smail.real /usr/sbin/smail
   fi

where "1.0-2" is the version at which the diversion was first added to
the package. The postrm should not remove the diversion on upgrades
both because there's no reason to remove the diversion only to
immediately re-add it and since the postrm of the old package is run
after unpacking so the removal of the diversion will fail.

Do not attempt to divert a file which is vitally important for the
system's operation - when using "dpkg-divert" there is a time, after
it has been diverted but before "dpkg" has installed the new version,
when the file does not exist.

Do not attempt to divert a conffile, as "dpkg" does not handle it
well.

Do not use diversions for files that have their own native override
mechanisms, such as "systemd" unit files. See Binary packages for more
information.



8. Debian Policy changes process
********************************


8.1. Introduction
=================

To introduce a change in the current Debian Policy, the change
proposal has to go through a certain process.  [1]


8.2. Change Goals
=================

* The change should be technically correct, and consistent with the
  rest of the policy document. This means no legislating the value of
  π. This also means that the proposed solution be known to work;
  iterative design processes do not belong in policy.

* The change should not be too disruptive; if very many packages
  become instantly buggy, then instead there should be a transition
  plan. Exceptions should be rare (only if the current state is really
  untenable), and probably blessed by the TC.

* The change has to be reviewed in depth, in the open, where any one
  may contribute; a publicly accessible, archived, open mailing list.

* Proposal should be addressed in a timely fashion.

* Any domain experts should be consulted, since not every policy
  mailing list subscriber is an expert on everything, including policy
  maintainers.

* The goal is rough consensus on the change, which should not be hard
  if the matter is technical. Technical issues where there is no
  agreement should be referred to the TC; non-technical issues should
  be referred to the whole developer body, and perhaps general
  resolutions lie down that path.

* Package maintainers whose packages may be impacted should have
  access to policy change proposals, even if they do not subscribe to
  policy mailing lists (policy gazette?).


8.3. Current Process
====================

Each suggested change goes through different states. These states are
denoted through either usertags of the debian-
policy@packages.debian.org user or, for "moreinfo", "patch",
"pending", and "wontfix", regular tags.

Current list of bugs

The Policy delegates are responsible for managing the tags on bugs and
will update tags as new bugs are submitted or as activity happens on
bugs. All Debian Developers should feel free to add the seconded tag
as described below. Other tags should be changed with the coordination
of the Policy Team.


8.3.1. State A: More information required
-----------------------------------------

The Policy delegates are unable to determine whether the bug is really
a Policy matter, or judge that there are missing details that would
prevent a fruitful discussion (and may result in a confused and
unhelpful discussion).

Policy delegates ask the original submitter to provide the missing
details.  Others are asked to refrain from discussing whatever they
take the issue to be, limiting their postings to attempts to supply
the missing details.

TAG: moreinfo

What needs to happen next: Submitter (or someone else) provides the
requested information within 30 days, or the bug is closed.

The majority of bugs will skip this stage.


8.3.2. State B: Discussion
--------------------------

Discuss remedy. Alternate proposals. Discussion guided by delegates.
There should be a clear time limit to this stage, but as yet we have
not set one.

TAG: discussion

What needs to happen next: Reach a conclusion and consensus in the
discussion and make a final proposal for what should be changed (if
anything), moving to the proposal tag.


8.3.3. State C: Proposal
------------------------

A final proposal has emerged from the discussion, and there is a rough
consensus on how to proceed to resolve the issue.

TAG: proposal

What needs to happen next: Provided that the rough consensus persists,
develop a patch against the current Policy document with specific
wording of the change. Often this is done in conjunction with the
proposal, in which case one may skip this step and move directly to
patch tag.


8.3.4. State D: Wording proposed
--------------------------------

A patch against the Policy document reflecting the consensus has been
created and is waiting for formal seconds. The standard patch tag is
used for this state, since it's essentially equivalent to the standard
meaning of that tag.

TAG: patch

What needs to happen next: The proposal needs to be reviewed and
seconded. Any Debian developer who agrees with the change and the
conclusion of rough consensus from the discussion should say so in the
bug log by seconding the proposal.


8.3.5. State E: Seconded
------------------------

The proposal is signed off on by N Debian Developers. To start with,
we're going with N=3, meaning that if three Debian Developers agree,
not just with the proposal but with the conclusion that it reflects
consensus and addresses the original issue -- it is considered
eligible for inclusion in the next version of Policy. Since Policy is
partly a technical project governance method, one must be a Debian
Developer to formally second, although review and discussion is
welcome from anyone. Once this tag has been applied, the bug is
waiting for a Policy team member to apply the patch to the package
repository.

TAG: seconded

What needs to happen next: A Policy maintainer does the final review
and confirmation, and then applies the patch for the next Policy
release.

This tag is not used very much because normally a Policy maintainer
applies the patch and moves the proposal to the next state once enough
seconds are reached.


8.3.6. State F: Accepted
------------------------

Change accepted, will be in next upload. The standard pending tag is
used for this state since it matches the regular meaning of pending.

TAG: pending

What needs to happen next: The bug is now in the waiting queue for the
next Policy release, and there's nothing left to do except for upload
a new version of Policy.


8.3.7. State G: Reject
----------------------

Rejected proposals. The standard wontfix is used for this state.
Normally, bugs in this state will not remain open (excepting
**stalled**); instead, a Policy team member will close them with an
explanation. The submitter may then appeal to the tech-ctte if they so
desire. Alternately, issues appealed to the tech-ctte may remain open
with this tag while that appeal proceeds.

TAG: wontfix

We may use one of the following tags here. It's not clear whether we
need more tags for this stage.

**dubious**
   Not a policy matter

**ctte**
   Referred to the Technical Committee (tech-ctte)

**devel**
   Referred to the developer body

**delegate**
   Rejected by a Policy delegate

**obsolete**
   Consensus on a proposal was not forthcoming, and the bug is to be
   closed.  Those wishing to restart discussion should open a new bug,
   but only if they have a concrete new change proposal.

**stalled**
   Consensus on a proposal was not forthcoming.  However, the bug
   should be kept open, as a form of documentation, and to minimise
   the number of duplicate filings.

What may need to happen next: The bug should be closed once a final
resolution is reached (excepting **stalled**), or retagged to an
appropriate state if that final resolution reverses the decision to
reject the proposal.


8.4. Other Tags
===============

All Policy bugs are additionally categorized by class of bug.

The normative tag is used for bugs that make normative changes to
Policy, meaning that the dictates of Policy will change in some
fashion as part of the resolution of the bug if the proposal is
accepted. The full process is followed for such bugs.

TAG: normative

The informative tag is used for bugs about wording issues, typos,
informative footnotes, or other changes that do not affect the formal
dictates of Policy, just the presentation. The same tags are used for
these bugs for convenience, but the Policy maintainers may make
informative changes without following the full process. Informative
bugs fall under their discretion.

TAG: informative

The packaging tag is used for bugs about the packaging and build
process of the debian-policy Debian package. These bugs do not follow
the normal process and will not have the other tags except for pending
and wontfix (used with their normal meanings).

TAG: packaging

[1] This process was originally developed by Margarita Manterola,
    Clint Adams, Russ Allbery and Manoj Srivastava.  In 2017, Sean
    Whitton deprecated the 'issue' usertag and added use of the
    'moreinfo' tag, after discussions at DebConf17.



9. Maintainer script flowcharts
*******************************

The flowcharts [1] included in this appendix use the following
conventions:

* maintainer scripts and their arguments are within boxes;

* actions carried out external to the scripts are in italics; and

* the "dpkg" status of the package at the end of the run are in bold
  type.

   [image: Installing a package that was not previously
   installed][image]Installing a package that was not previously
   installed

   [image: Installing a package that was previously removed, but not
   purged][image]Installing a package that was previously removed, but
   not purged

   [image: Upgrading a package][image]Upgrading a package

   [image: Removing a package][image]Removing a package

   [image: Purging a package previously removed][image]Purging a
   package previously removed

   [image: Removing and purging a package][image]Removing and purging
   a package

[1] These flowcharts were originally created by Margarita Manterola
    for the Debian Women project wiki.



10. Upgrading checklist
***********************


10.1. About the checklist
=========================

The checklist below has been created to simplify the upgrading process
of old packages. This list is not official or normative. It only
provides an indication of what has changed and whether you are likely
to need to make changes to your package in light of this. If you have
doubts about a certain topic, if you need more details, or if you
think some other package does not comply with policy, please refer to
the Policy Manual itself.

All of the changes from version 3.0.0 onwards indicate which section
of the Policy Manual discusses the issue. The section numbering should
still be accurate for changes back to the 2.5.0 release. Before that
point, the sections listed here probably no longer correspond to
sections in the modern Policy Manual.

Here is how the check list works: Check which policy version your
package was checked against last (indicated in the "Standards-Version"
field of the source package). Then move upwards until the top and
check which of the items on the list might concern your package. Note
which sections of policy discuss this, and then check out the Policy
Manual for details. Once you've made all necessary changes to match
the current rules, update the value of "Standards-Version" to the
current Policy Manual version.

If an item in the list is followed by the name of a Lintian tag in
square brackets, it indicates that the policy requirement is covered
by that Lintian tag.  The lack of such an annotation does not mean
that no Lintian tag exists to cover the requirement.  Our coverage of
these annotations is quite incomplete, and patches to this checklist
are very welcome.

The sections in this checklist match the values for the "Standards-
Version" control field in omitting the minor patch version, except in
the two anomalous historical cases where normative requirements were
changed in a minor patch release.


10.2. Version 4.7.4
===================

Released March, 2026.

8.4
   "*.so" files in shared library development packages may be linker
   scripts instead of symbolic links.  See the relevant section for
   the constraints on linker scripts required by **ldconfig**.

12.5
   The requirement to explain in the copyright file why the package is
   not part of the Debian distribution also applies to packages in
   *non-free-firmware*.


10.3. Version 4.7.3
===================

Released December, 2025.

5.6.6
   Specifying the "Priority" field in source package control fields is
   no longer recommended unless the priority needs to be changed from
   the default.  If the field is omitted, the default source package
   priority is "optional", and binary packages inherit the priority
   from the source package.

5.6.32 & 5.6.33
   New sections documenting the "Git-Tag-Tagger" and "Git-Tag-Info"
   fields in Debian source control and ".changes" files.


10.4. Version 4.7.2
===================

Released February, 2025.

10.1
   A change made the previous release of Policy is relaxed:

   Packages that already install programs to /usr/games, where another
   package installs a program of the same name with different
   functionality to a different directory on the default PATH, may
   continue to do so.

   Packages must not install any newly conflicting programs to
   /usr/games, and packages already doing so are encouraged to move
   these programs to non-conflicting names.


10.5. Version 4.7.1
===================

Released February, 2025.

10.1
   Two different packages must not install programs with different
   functionality to the same filenames, even names under different
   directories, when the directories are on the default PATH.

10.1
   Packages must not install files to directories like /bin, /lib,
   /lib* and /sbin which are now symbolic links to corresponding
   directories under /usr.  Packages may assume that /bin, /lib and
   /sbin are always symlinks, and that files under /usr/bin, /usr/lib
   and /usr/sbin are accessible via these aliases.

10.9
   Packages should not require the existence of any files under
   /usr/share/locale in order to function in a C or C.UTF-8 locale.

12.1
   Packages (other than manpage readers) must not require the
   existence of any files under /usr/share/man.

12.2
   Packages (other than info readers) must not require the existence
   of any files in /usr/share/info.


10.6. Version 4.7.0
===================

Released April, 2024.

2.2.1
   Document that source packages in the *main* archive area may build
   binary packages in the *contrib* archive area, although this is
   discouraged unless the source package is inconvenient to split.
   This does not relax the requirement that source packages in *main*
   must not have build dependencies outside of *main*.

2.2.2
   The "non-free-firmware" archive area has been added.

3.9
   Maintainer scripts should use native overriding mechanisms instead
   of dpkg-divert, wherever possible.  Maintainer scripts must not
   divert configuration files used by systemd components.

   Maintainer scripts must not use the alternatives system for systemd
   configuration files.

4.8
   Hard links are permitted in source packages.

4.9
   For packages in contrib, and for packages in non-free with
   "Autobuild: yes", required targets in d/rules are no longer
   permitted to attempt network access.  Previously, only packages in
   main had this restriction.

5.6.13
   The "Description" field is not present in ".changes" files if no
   binary packages are being uploaded.

5.6.19
   The "Binary" field is not present in ".changes" files if no binary
   packages are being uploaded.

6.3
   Packages that automatically start or stop system services must
   include "systemd" units unless the service is only intended for use
   on systems running alternative init systems.  Previously, "systemd"
   also supported init scripts, but that support is being removed.


10.7. Version 4.6.2
===================

Released December, 2022.

3.8
   Essential packages are only required to provide their core
   functionality when unconfigured if they had previously been
   configured at least once.

6.5 & 6.6
   The new package version is provided as an additional argument
   following the old package version to several "preinst", "prerm",
   and "postrm" maintainer script actions.

11.8.4
   When computing the priority for alternatives for "/usr/bin/x
   -window-manager", start with a priority of 40, not 20, and don't
   increase the priority based on support for the (obsolete) Debian
   menu system.


10.8. Version 4.6.1
===================

Released May, 2022.

9.1.1
   Restore permission for packages for non-64-bit architectures to
   install files to "/usr/lib64/".

9.7.2 & 9.7.3
   The text of these sections has been updated to reflect the package
   split of bin:mime-support into bin:media-types and bin:mailcap.


10.9. Version 4.6.0
===================

Released August, 2021.

9.1.1
   No package is allowed to install files in "/usr/lib64/".
   Previously, this prohibition only applied to packages for 64-bit
   architectures.

12.1
   Manual pages may be included in dependencies, not only in the
   packages containing the things they document.


10.10. Version 4.5.1
====================

Released November, 2020.

2.3, 4.5 & 12.5
   The copyright information for files in a package must be copied
   verbatim into "/usr/share/doc/PACKAGE/copyright" when all of the
   following hold:

   1. the distribution license for those files requires that copyright
      information be included in all copies and/or binary
      distributions;

   2. the files are shipped in the binary package, either in source or
      compiled form; and

   3. the form in which the files are present in the binary package
      does not include a plain text version of their copyright
      notices.

   Note that there is no change to the requirement to copy all
   licensing information into "/usr/share/doc/PACKAGE/copyright".

   (Previously, it was always required for all copyright information
   to be copied into "/usr/share/doc/PACKAGE/copyright".)

4.17
   Packages must not contain a non-default series file.  That is,
   dpkg's vendor-specific patch series feature must not be used for
   packages in the Debian archive.

   (previously a "should not")


10.11. Version 4.5.0
====================

Released January, 2020.

9.2.1
   When maintainers choose a new hardcoded or dynamically generated
   username for packages to use, they should start this username with
   an underscore.

9.3.1
   Packages that include system services should include "systemd"
   service units to start or stop those services.

   Including an init script is encouraged if there is no systemd unit,
   and optional if there is (previously, it was recommended).

   In the common case that a package includes a single system service,
   the service unit should have the same name as the package plus the
   ".service" extension.  If an init script is included, it should
   have the same name as the systemd unit.

9.3.2
   It is encouraged for init scripts to support the "status" argument
   (previously, it was recommended).

9.3.3
   Use of update-rc.d is required if the package includes an init
   script (previously, Policy said in one place that it was required,
   and in another said that it was recommended).


10.12. Version 4.4.1
====================

Released September, 2019.

5.6.26
   A package control file must not have more than one "Vcs-<type>"
   field.

   If the package is maintained in multiple version control systems,
   the maintainer should specify the one that they would prefer other
   people to use as the basis for proposing changes to the package.

9.10 & 11.5
   doc-base registration is now optional, from being recommended.

9.12
   Document "/run/reboot-required" mechanism.

copyright-format
   State some syntactical restrictions on the "Files:" field.
   Wildcards are required to match the contents of directories, and
   the space character separates patterns and cannot be escaped.


10.13. Version 4.4.0
====================

Released July, 2019.

4.9
   The recommended way to implement the build process of a Debian
   package, in the absence of a good reason to use a different
   approach, is the "dh" tool.  This recommendation includes the
   contents of the "debian/rules" building script.

   Some examples of good reasons to use a different approach are
   given.  The recommendation to use "dh" does not always apply, and
   use of "dh" is not required.

5.6.26
   Permit "-b" in Vcs-Hg as well as Vcs-Git.

7.5
   Document versioned Provides.

virtual
   New "logind" and "default-logind" virtual packages for a package
   providing logind API (via D-Bus and *sd-login(3)*), and for
   Debian's preferred implementation, respectively.


10.14. Version 4.3.0
====================

Released December, 2018.

2.3 & 4.5
   In cases where a package's distribution license explicitly permits
   its copyright information to be excluded from distributions of
   binaries built from the source, a verbatim copy of the package's
   copyright information should normally still be included in the
   copyright file, but it need not be if creating and maintaining a
   copy of that information involves significant time and effort.

4.9
   Required targets must not write outside of the unpacked source
   package tree, except for TMPDIR, /tmp and /var/tmp.

4.17
   Packages should not contain a non-default series file.  That is,
   dpkg's vendor-specific patch series feature should not be used for
   packages in the Debian archive.

10.1
   Binaries should be stripped using "strip --strip-unneeded --remove-
   section=.comment --remove-section=.note" (as dh_strip already
   does).

10.1
   It is no longer suggested nor recommended to use "install -s" to
   strip binaries, because it gets several things wrong.

10.2
   When stripping shared libraries with *strip(1)*, you should
   additionally pass "--remove-section=.comment --remove-
   section=.note" (as dh_strip already does).

virtual
   New "dbus-session-bus" and "default-dbus-session-bus" virtual
   packages for a package providing the D-Bus session bus, and for
   Debian's preferred D-Bus implementation, respectively.


10.15. Version 4.2.1
====================

Released August, 2018.

10.4 & perl
   The requirement that the shebang at the top of Perl command scripts
   be "#!/usr/bin/perl" is relaxed from a 'must' to a 'should'.


10.16. Version 4.2.0
====================

Released August, 2018.

4.9
   The package build should be as verbose as reasonably possible. This
   means that "debian/rules" should pass to the commands it invokes
   options that cause them to produce verbose output.

4.9
   Required targets may attempt network access, via the loopback
   interface, to services on the build host that have been started by
   the build.

4.9.1
   New "terse" tag that can appear in "DEB_BUILD_OPTIONS" to make a
   package build less verbose.

5.2 & 5.4
   The Standards-Version field is now mandatory, not just recommended.

12.7
   Upstream release notes, when available, should be installed as
   "/usr/share/doc/package/NEWS.gz".  Upstream changelogs may be made
   available as "/usr/share/doc/package/changelog.gz".

   This is a relaxation of older Policy which said that the upstream
   changelog should be made accessible at this path.  Now it is up to
   maintainer discretion whether it is useful to install it.

   The practice of installing the upstream release notes as
   "/usr/share/doc/package/changelog.gz" is permitted but deprecated.


10.17. Version 4.1.5
====================

Released July, 2018.

4.9.2
   Document how "debian/rules" and the "Rules-Requires-Root" field
   interact.

5.6.12
   You should not change a package's epoch, even in experimental,
   without getting consensus on debian-devel first.

5.6.12.1
   Epochs should not be used for the purpose of rolling back the
   version of a package.  Use the +really convention.

5.6.31
   Document the "Rules-Requires-Root" field.

9.1.1
   Update Debian's version of the Filesystem Hierarchy Standard from
   2.3 to 3.0, and update the list of exceptions.  Only a tiny
   minority of packages, if any, should be made buggy by this change.

9.3.2 & 10.4
   Update version of POSIX standard for shell scripts from SUSv3 to
   POSIX.1-2017 (also known as SUSv4 in some contexts).


10.18. Version 4.1.4
====================

Released April, 2018.

3.2.2
   The part of the version number after the epoch must not be reused
   for a version of the package with different contents, even after
   the version of the package previously using that part of the
   version number is no longer present in any archive suites.

3.2.2
   For non-native packages, the upstream version must not be reused
   for different upstream source code, so that for each source package
   name and upstream version number there exists exactly one original
   source archive contents.

4.9
   The "get-orig-source" rules target has been removed.  Packages
   should transition to "debian/watch" and use uscan where possible.

9.1.2
   If "/etc/staff-group-for-usr-local" does not exist, "/usr/local"
   and all subdirectories created by packages should have permissions
   0755 and be owned by "root:root".  If the file exists, the old
   permissions of 2775 and ownership of root:staff should remain.


10.19. Version 4.1.3
====================

Released December, 2017.

5.6.26
   URLs given in "VCS-*" headers should use a scheme that provides
   confidentiality ("https", for example) if the VCS repository
   supports it.  "[vcs-field-uses-insecure-uri]"

7.8
   "Built-Using" should be used exactly when there are license or DFSG
   requirements to retain full source code in the archive. Previously,
   the description of the field implied it was needed in other cases
   too.

9.1.1
   "libc" may also install files in "/lib64".

9.3.3.1
   If a package's daemon should not be autostarted unless the local
   administrator has explicitly requested it, the package's "postinst"
   should use the new "defaults-disabled" option of "update-rc.d".

   The old method of including "DISABLED=yes" in the package's
   "/etc/default" file should not be used.

11.4
   Clarify that programs may invoke either "/usr/bin/editor" and
   "/usr/bin/pager" directly, or use "editor" and "pager" and rely on
   PATH.

12.5
   The Creative Commons CC0 1.0 Universal license (CC0-1.0) is now
   included in "/usr/share/common-licenses" and does not need to be
   copied verbatim in the package "copyright" file.


10.20. Version 4.1.2
====================

Released November, 2017.

3.1.1
   Binary packages that have potentially offensive content should have
   the suffix "-offensive".  This replaces an older convention to use
   "-off".  As before, whether the contents of a package needs this
   content warning is a matter of maintainer discretion.

10.2
   Private shared object files should be installed in subdirectories
   of "/usr/lib" or "/usr/lib/triplet".  This change permits private
   shared object files to take advantage of multiarch, and also
   removes the implication that it is permissible to install private
   shared object files directly into "/usr/lib/triplet".

10.4
   The shebang at the top of Perl command scripts must be
   "#!/usr/bin/perl".  (Previously, this was a 'should' rather than a
   'must'.)


10.21. Version 4.1.1
====================

Released September, 2017.

4.4
   debian/changelog must exist in source packages.

9.2.3
   The canonical non-existent home directory is "/nonexistent".


10.22. Version 4.1.0
====================

Released August, 2017.

2.2.1
   Non-default alternative dependencies on non-free packages are
   permitted for packages in main.

4.11
   If upstream provides OpenPGP signatures, including the upstream
   signing key as "debian/upstream/signing-key.asc" in the source
   package and using the "pgpsigurlmangle" option in "debian/watch"
   configuration to indicate how to find the upstream signature for
   new releases is recommended.

4.15
   Packages should build reproducibly when certain factors are held
   constant; see 4.15 for the list.

4.15
   Packages are recommended to build reproducibly even when build
   paths and most environment variables are allowed to vary.

9.1.1
   Only the dynamic linker may install files to "/lib64/".

   No package for a 64 bit architecture may install files to
   "/usr/lib64/" or any subdirectory.

11.8.3
   The required behaviour of "x-terminal-emulator -e" has been
   clarified, and updated to replace a false claim about the behaviour
   of "xterm".

   Programs must support "-e command" where "command" may include
   multiple arguments, which must be executed as if the arguments were
   passed to "execvp" directly, bypassing the shell.

   If this execution fails and "-e" has a single argument, "xterm"'s
   fallback behaviour of passing "command" to the shell is permitted
   but not required.


10.23. Version 4.0.1
====================

Released August, 2017.

2.5
   Priorities are now used only for controlling which packages are
   part of a minimal or standard Debian installation and should be
   selected based on functionality provided directly to users (so
   nearly all shared libraries should have a priority of "optional").
   Packages may now depend on packages with a lower priority.

   The "extra" priority has been deprecated and should be treated as
   equivalent to "optional". All "extra" priorities should be changed
   to "optional". Packages with a priority of "optional" may conflict
   with each other (but packages that both have a priority of
   "standard" or higher still may not conflict).

5.6.30
   New section documenting the "Testsuite" field in Debian source
   control files.

8.1.1
   Shared libraries must now invoke "ldconfig" by means of triggers,
   instead of maintscripts.

9.3.3
   Packages are recommended to use debhelper tools instead of invoking
   "update-rc.d" and "invoke-rc.d" directly.

9.3.3
   Policy's description of how the local system administrator may
   modify the runlevels at which a daemon is started and stopped, and
   how init scripts may depend on other init scripts, have been
   removed. These are now handled by LSB headers.

9.4
   Policy's specification of the console messages that should be
   emitted by "init.d" scripts has been removed. This is now defined
   by LSB, for sysvinit, and is not expected to be followed by other
   init systems.

9.6
   Packages installing a Free Desktop entry must not also install a
   Debian menu system entry.

9.9
   The prohibition against depending on environment variables for
   reasonable defaults is only for programs on the system PATH and
   only for custom environment variable settings (not, say, a sane
   PATH).


10.24. Version 4.0.0
====================

Released May, 2017.

4.3
   "config.sub" and "config.guess" should be updated at build time or
   replaced with the versions from autotools-dev.

4.9
   New "TARGET" set of "dpkg-architecture" variables and new
   "DEB_*_ARCH_BITS" and "DEB_*_ARCH_ENDIAN" variables.

4.9.1
   New "DEB_BUILD_OPTIONS" tag, "nodoc", which says to suppress
   documentation generation (but continue to build all binary
   packages, even documentation packages, just let them be mostly
   empty).

5.2
   Automatically-generated debug packages do not need to have a
   corresponding stanza in "debian/control". (This is existing
   practice; this Policy update is just clearer about it.)

5.6.12
   Colons are not permitted in upstream version numbers.

7.7
   New "Build-Depends-Arch" and "Build-Conflicts-Arch" fields are now
   supported.

8.4
   The recommended package name for shared library development files
   is now libraryname-dev or librarynameapiversion-dev, not
   librarynamesoversion-dev.

9.1.1
   The stable release of Debian supports "/run", so packages may now
   assume that it exists and do not need any special dependency on a
   version of initscripts.

9.3.2
   New optional "try-restart" standard init script argument, which (if
   supported) should restart the service if it is already running and
   otherwise just report success.

9.3.2
   Support for the "status" init script argument is recommended.

9.3.3.2
   Packages must not call "/etc/init.d" scripts directly even as a
   fallback, and instead must always use "invoke-rc.d" (which is
   essential and shouldn't require any conditional).

9.11.1
   Instructions for "upstart" integration removed since "upstart" is
   no longer maintained in Debian.

10.1
   Packages may not install files in both "/path" and "/usr/path", and
   must manage any backward-compatibility symlinks so that they don't
   break if "/path" and "/usr/path" are the same directory.

10.6
   Packages should assume device files in "/dev" are dynamically
   managed and don't have to be created by the package. Packages other
   than those whose purpose is to manage "/dev" must not create or
   remove files there when a dynamic management facility is in use.
   Named pipes and device files outside of "/dev" should normally be
   created on demand via init scripts, systemd units, or similar
   mechanisms, but may be created and removed in maintainer scripts if
   they must be created during package installation.

10.9
   Checking with the base-passwd maintainer is no longer required (or
   desirable) when creating a new dynamic user or group in a package.

12.3
   Dependencies on *-doc packages should be at most Recommends
   (Suggests if they only include documentation in supplemental
   formats).

12.5
   The Mozilla Public License 1.1 and 2.0 (MPL-1.1 and MPL-2.0) are
   now included in "/usr/share/common-licenses" and do not need to be
   copied verbatim in the package "copyright" file.

copyright-format
   The "https" form of the copyright-format URL is now allowed and
   preferred in the "Format" field.

perl
   The Perl search path now includes multiarch directories. The vendor
   directory for architecture-specific modules is now versioned to
   support multiarch.

virtual
   New "adventure" virtual package for implementations of the classic
   Colossal Cave Adventure game.

virtual
   New "httpd-wsgi3" virtual package for Python 3 WSGI-capable HTTP
   servers. The existing "httpd-wsgi" virtual package is for Python 2
   WSGI-capable HTTP servers.

virtual
   New "virtual-mysql-client", "virtual-mysql-client-core", "virtual-
   mysql-server", "virtual-mysql-server-core", and "virtual-mysql-
   testsuite" virtual packages for MySQL-compatible software.


10.25. Version 3.9.8
====================

Released April, 2016.

9.6
   The menu system is deprecated in favor of the FreeDesktop menu
   standard. New requirements set for FreeDesktop menu entries.

9.7
   New instructions for registering media type handlers with the
   FreeDesktop system, which automatically synchronizes with mailcap
   and therefore replaces mailcap registration for packages using
   desktop entries.


10.26. Version 3.9.7
====================

Released February, 2016.

10.5
   Symbolic links must not traverse above the root directory.

9.2.2
   32bit UIDs in the range 65536-4294967293 are reserved for
   dynamically allocated user accounts.

5.1
   Empty field values in control files are only permitted in the
   "debian/control" file of a source package.

4.9
   "debian/rules": required targets must not attempt network access.

12.3
   recommend to ship additional documentation for package "pkg" in a
   separate package "pkg-doc" and install it into
   "/usr/share/doc/pkg".


10.27. Version 3.9.6
====================

Released September, 2014.

9.1
   The FHS is relaxed to allow a subdirectory of "/usr/lib" to hold a
   mixture of architecture-independent and architecture-dependent
   files, though directories entirely composed of architecture-
   independent files should be located in "/usr/share".

9.1
   The FHS requirement for "/usr/local/lib64" to exist if "/lib64" or
   "/usr/lib64" exists is removed.

9.1
   An FHS exception has been granted for multiarch include files,
   permitting header files to instead be installed to
   "/usr/include/triplet".

10.1
   Binaries must not be statically linked with the GNU C library, see
   policy for exceptions.

4.4
   It is clarified that signature appearing in debian/changelog should
   be the details of the person who prepared this release of the
   package.

11.5
   The default web document root is now "/var/www/html"

virtual
   "java1-runtime" and "java2-runtime" are removed, "javaN-runtime"
   and "javaN-runtime-headless" are added for all N between 5 and 9.

virtual
   Added "httpd-wsgi" for WSGI capable HTTP servers.

perl
   Perl packages should use the "%Config" hash to locate module paths
   instead of hardcoding paths in "@INC".

perl
   Perl binary modules and any modules installed into
   "$Config{vendorarch}" must depend on the relevant perlapi-*
   package.


10.28. Version 3.9.5
====================

Released October, 2013.

5.1
   Control data fields must not start with the hyphen character ("-"),
   to avoid potential confusions when parsing clearsigned control data
   files that were not properly unescaped.

5.4, 5.6.24
   "Checksums-Sha1" and "Checksums-Sha256" are now mandatory in ".dsc"
   files.

5.6.25, 5.8.1
   The "DM-Upload-Allowed" field is obsolete. Permissions are now
   granted via *dak-commands* files.

5.6.27
   New section documenting the "Package-List" field in Debian source
   control files.

5.6.28
   New section documenting the "Package-Type" field in source package
   control files.

5.6.29
   New section documenting the "Dgit" field in Debian source control
   files.

9.1.1.8
   The exception to the FHS for the "/selinux" was removed.

10.7.3
   Packages should remove all obsolete configuration files without
   local changes during upgrades. The "dpkg-maintscript-helper" tool,
   available from the dpkg package since *Wheezy*, can help with this.

10.10
   The name of the files and directories installed by binary packages
   must be encoded in UTF-8 and should be restricted to ASCII when
   possible. In the system PATH, they must be restricted to ASCII.

11.5.2
   Stop recommending to serve HTML documents from
   "/usr/share/doc/package".

12.2
   Packages distributing Info documents should use install-info's
   trigger, and do not need anymore to depend on "dpkg (>= 1.15.4) |
   install-info".

debconf
   The "escape" capability is now documented.

virtual
   "mp3-decoder" and "mp3-encoder" are removed.


10.29. Version 3.9.4
====================

Released August, 2012.

2.4
   New *tasks* archive section.

4.9
   "build-arch" and "build-indep" are now mandatory targets in
   "debian/rules".

5.6.26
   New section documenting the "Vcs-*" fields, which are already in
   widespread use. Note the mechanism for specifying the Git branch
   used for packaging in the Vcs-Git field.

7.1
   The deprecated relations < and > now must not be used.

7.8
   New "Built-Using" field, which must be used to document the source
   packages for any binaries that are incorporated into this package
   at build time. This is used to ensure that the archive meets
   license requirements for providing source for all binaries.

8.6
   Policy for dependencies between shared libraries and other packages
   has been largely rewritten to document the "symbols" system and
   more clearly document handling of shared library ABI changes.
   "symbols" files are now recommended over "shlibs" files in most
   situations. All maintainers of shared library packages should
   review the entirety of this section.

9.1.1
   Packages must not assume the "/run" directory exists or is usable
   without a dependency on "initscripts (>= 2.88dsf-13.3)" until the
   stable release of Debian supports "/run".

9.7
   Packages including MIME configuration can now rely on triggers and
   do not need to call update-mime.

9.11
   New section documenting general requirements for alternate init
   systems and specific requirements for integrating with upstart.

12.5
   All copyright files must be encoded in UTF-8.


10.30. Version 3.9.3
====================

Released February, 2012.

2.4
   New archive sections *education*, *introspection*, and
   *metapackages* added.

5.6.8
   The "Architecture" field in "*.dsc" files may now contain the value
   "any all" for source packages building both architecture-
   independent and architecture-dependent packages.

7.1
   If a dependency is restricted to particular architectures, the list
   of architectures must be non-empty.

9.1.1
   "/run" is allowed as an exception to the FHS and replaces
   "/var/run". "/run/lock" replaces "/var/lock". The FHS requirements
   for the older directories apply to these directories as well.
   Backward compatibility links will be maintained and packages need
   not switch to referencing "/run" directly yet. Files in "/run"
   should be stored in a temporary file system.

9.1.4
   New section spelling out the requirements for packages that use
   files in "/run", "/var/run", or "/var/lock". This generalizes
   information previously only in 9.3.2.

9.5
   Cron job file names must not contain "." or "+" or they will be
   ignored by cron. They should replace those characters with "_". If
   a package provides multiple cron job files in the same directory,
   they should each start with the package name (possibly modified as
   above), "-", and then some suitable suffix.

9.10
   Packages using doc-base do not need to call install-docs anymore.

10.7.4
   Packages that declare the same "conffile" may see left-over
   configuration files from each other even if they conflict.

11.8
   The Policy rules around Motif libraries were just a special case of
   normal rules for non-free dependencies and were largely obsolete,
   so they have been removed.

12.5
   "debian/copyright" is no longer required to list the Debian
   maintainers involved in the creation of the package (although note
   that the requirement to list copyright information is unchanged).

copyright-format
   Version 1.0 of the "Machine-readable "debian/copyright" file"
   specification is included.

mime
   This separate document has been retired and and its (short)
   contents merged into Policy section 9.7. There are no changes to
   the requirements.

perl
   Packages may declare an interest in the perl-major-upgrade trigger
   to be notified of major upgrades of perl.

virtual
   "ttf-japanese-{mincho, gothic}" is renamed to "fonts-
   japanese-{mincho, gothic}".


10.31. Version 3.9.2
====================

Released April, 2011.

*
   Multiple clarifications throughout Policy where "installed" was
   used and the more precise terms "unpacked" or "configured" were
   intended.

3.3
   The maintainer address must accept mail from Debian role accounts
   and the BTS. At least one human must be listed with their personal
   email address in "Uploaders" if the maintainer is a shared email
   address. The duties of a maintainer are also clearer.

5
   All control fields are now classified as simple, folded, or
   multiline, which governs whether their values must be a single line
   or may be continued across multiple lines and whether line breaks
   are significant.

5.1
   Parsers are allowed to accept stanza separation lines containing
   whitespace, but control files should use completely empty lines.
   Ordering of stanzas is significant. Field names must be composed of
   printable ASCII characters except colon and must not begin with #.

5.6.25
   The "DM-Upload-Allowed" field is now documented.

6.5
   The system state maintainer scripts can rely upon during each
   possible invocation is now documented. In several less-common
   cases, this is stricter than Policy had previously documented.
   Packages with complex maintainer scripts should be reviewed in
   light of this new documentation.

7.2
   The impact on system state when maintainer scripts that are part of
   a circular dependency are run is now documented. Circular
   dependencies are now a should not.

7.2
   The system state when "postinst" and "prerm" scripts are run is now
   documented, and the documentation of the special case of dependency
   state for "postrm" scripts has been improved. "postrm" scripts are
   required to gracefully skip actions if their dependencies are not
   available.

9.1.1
   GNU/Hurd systems are allowed "/hurd" and "/servers" directories in
   the root filesystem.

9.1.1
   Packages installing to architecture-specific subdirectories of
   "/usr/lib" must use the value returned by "dpkg-architecture
   -qDEB_HOST_MULTIARCH", not by "dpkg-architecture
   -qDEB_HOST_GNU_TYPE"; this is a path change on i386 architectures
   and a no-op for other architectures.

virtual
   "mailx" is now a virtual package provided by packages that install
   "/usr/bin/mailx" and implement at least the POSIX-required
   interface.


10.32. Version 3.9.1
====================

Released July, 2010.

3.2.1
   Date-based version components should be given as the four-digit
   year, two-digit month, and then two-digit day, but may have
   embedded punctuation.

3.9
   Maintainer scripts must pass "--package" to "dpkg-divert" when
   creating or removing diversions and must not use "--local".

4.10
   Only "dpkg-gencontrol" supports variable substitution. "dpkg-
   genchanges" (for "*.changes") and "dpkg-source" (for "*.dsc") do
   not.

7.1
   Architecture restrictions and wildcards are also allowed in binary
   package relationships provided that the binary package is not
   architecture-independent.

7.4
   "Conflicts" and "Breaks" should only be used when there are file
   conflicts or one package breaks the other, not just because two
   packages provide similar functionality but don't interfere.

8.1
   The SONAME of a library should change whenever the ABI of the
   library changes in a way that isn't backward-compatible. It should
   not change if the library ABI changes are backward-compatible.
   Discourage bundling shared libraries together in one package.

8.4
   Ada Library Information ("*.ali") files must be installed read-
   only.

8.6.1, 8.6.2, 8.6.5
   Packages should normally not include a "shlibs.local" file since we
   now have complete "shlibs" coverage.

8.6.3
   The SONAME of a library may instead be of the form "name-major-
   version.so".

10.2
   Libtool ".la" files should not be installed for public libraries.
   If they're required (for "libltdl", for instance), the
   "dependency_libs" setting should be emptied. Library packages
   historically including ".la" files must continue to include them
   (with "dependency_libs" emptied) until all libraries that depend on
   that library have removed or emptied their ".la" files.

10.2
   Libraries no longer need to be built with "-D_REENTRANT", which was
   an obsolete LinuxThreads requirement. Instead, say explicitly that
   libraries should be built with threading support and to be thread-
   safe if the library supports this.

10.4
   "/bin/sh" scripts may assume that "kill" supports an argument of
   "-signal", that "kill" and "trap" support the numeric signals
   listed in the XSI extension, and that signal 13 (SIGPIPE) can be
   trapped with "trap".

10.8
   Use of "/etc/logrotate.d/package" for logrotate rules is now
   recommended.

10.9
   Control information files should be owned by "root:root" and either
   mode 644 or mode 755.

11.4, 11.8.3, 11.8.4
   Packages providing alternatives for "editor", "pager", "x-terminal-
   emulator", or "x-window-manager" should also provide a slave
   alternative for the corresponding manual page.

11.5
   Cgi-bin executable files may be installed in subdirectories of
   "/usr/lib/cgi-bin" and web servers should serve out executables in
   those subdirectories.

12.5
   The GPL version 1 is now included in common-licenses and should be
   referenced from there instead of included in the "copyright" file.


10.33. Version 3.9.0
====================

Released June, 2010.

4.4, 5.6.15
   The required format for the date in a changelog entry and in the
   Date control field is now precisely specified.

5.1
   A control stanza must not contain more than one instance of a
   particular field name.

5.4, 5.5, 5.6.24
   The "Checksums-Sha1" and "Checksums-Sha256" fields in "*.dsc" and
   "*.changes" files are now documented and recommended.

5.5, 5.6.16
   The "Format" field of ".changes" files is now 1.8. The "Format"
   field syntax for source package ".dsc" files allows a subtype in
   parentheses, and it is used for a different purpose than the
   "Format" field for ".changes" files.

5.6.2
   The syntax of the "Maintainer" field is now must rather than
   should.

5.6.3
   The comma separating entries in "Uploaders" is now must rather than
   should.

5.6.8, 7.1, 11.1.1
   Architecture wildcards may be used in addition to specific
   architectures in "debian/control" and "*.dsc" Architecture fields,
   and in architecture restrictions in build relationships.

6.3
   Maintainer scripts are no longer guaranteed to run with a
   controlling terminal and must be able to fall back to
   noninteractive behavior (debconf handles this). Maintainer scripts
   may abort if there is no controlling terminal and no reasonable
   default for a high-priority question, but should avoid this if
   possible.

7.3, 7.6.1
   "Breaks" should be used with "Replaces" for moving files between
   packages.

7.4
   "Breaks" should normally be used instead of "Conflicts" for
   transient issues and moving files between packages. New
   documentation of when each should be used.

7.5
   Use "Conflicts" with "Provides" if only one provider of a virtual
   facility can be installed at a time.

8.4
   All shared library development files are no longer required to be
   in the "-dev" package, only be available when the "-dev" package is
   installed. This allows the "-dev" package to be split as long as it
   depends on the additional packages.

9.2.2
   The UID range of user accounts is extended to 1000-59999.

9.3.2, 10.4
   "init.d" scripts are a possible exception from the normal
   requirement to use "set -e" in each shell script.

12.5
   The UCB BSD license was removed from the list of licenses that
   should be referenced from "/usr/share/common-licenses/BSD". It
   should instead be included directly in "debian/copyright", although
   it will still be in common-licenses for the time being.

debconf
   "SETTITLE" is now documented (it has been supported for some time).
   "SETTITLE" is like "TITLE" but takes a template instead of a string
   to allow translation.

perl
   perl-base now provides perlapi-abiname instead of a package based
   solely on the Perl version. Perl packages must now depend on
   perlapi-$Config{debian_abi}, falling back on "$Config{version}" if
   "$Config{debian_abi}" is not set.

perl
   Packages using "Makefile.PL" should use "DESTDIR" rather than
   "PREFIX" to install into the package staging area. "PREFIX" only
   worked due to a Debian-local patch.


10.34. Version 3.8.4
====================

Released January, 2010.

9.1.1
   An FHS exception has been granted for multiarch libraries.
   Permitting files to instead be installed to "/lib/triplet" and
   "/usr/lib/triplet" directories.

10.6
   Packages may not contain named pipes and should instead create them
   in postinst and remove them in prerm or postrm.

9.1.1
   "/sys" and "/selinux" directories are explicitly allowed as an
   exception to the FHS.


10.35. Version 3.8.3
====================

Released August, 2009.

4.9
   DEB_*_ARCH_CPU and DEB_*_ARCH_OS variables are now documented and
   recommended over GNU-style variables for that information.

5.6.8
   Source package Architecture fields may contain *all* in combination
   with other architectures. Clarify when *all* and *any* may be used
   in different versions of the field.

5.6.14
   The Debian archive software does not support uploading to multiple
   distributions with one "*.changes" file.

5.6.19
   The Binary field may span multiple lines.

10.2
   Shared library packages are no longer allowed to install libraries
   in a non-standard location and modify "ld.so.conf". Packages should
   either be installed in a standard library directory or packages
   using them should be built with RPATH.

11.8.7
   Installation directories for X programs have been clarified.
   Packages are no longer required to pre-depend on x11-common before
   installing into "/usr/include/X11" and "/usr/lib/X11".

12.1
   Manual pages are no longer required to contain only characters
   representable in the legacy encoding for that language.

12.1
   Localized man pages should either be kept up-to-date with the
   original version or warn that they're not up-to-date, either with
   warning text or by showing missing or changed portions in the
   original language.

12.2
   install-info is now handled via triggers so packages no longer need
   to invoke it in maintainer scripts. Info documents should now have
   directory sections and entries in the document. Packages containing
   info documents should add a dependency to support partial upgrades.

perl
   The requirement for Perl modules to have a versioned Depend and
   Build-Depend on "perl >= 5.6.0-16" has been removed.


10.36. Version 3.8.2
====================

Released June, 2009.

2.4
   The list of archive sections has been significantly expanded. See
   this debian-devel-announce message for the list of new sections and
   rules for how to categorize packages.

3.9.1
   All packages must use debconf or equivalent for user prompting,
   though essential packages or their dependencies may also fall back
   on other methods.

5.6.1
   The requirements for source package names are now explicitly
   spelled out.

9.1
   Legacy XFree86 servers no longer get a special exception from the
   FHS permitting "/etc/X11/XF86Config-4".

9.1.3
   Removed obsolete dependency requirements for packages that use
   "/var/mail".

11.8.5
   Speedo fonts are now deprecated. The X backend was disabled
   starting in lenny.

12.5
   The GNU Free Documentation License version 1.3 is included in
   common-licenses and should be referenced from there.


10.37. Version 3.8.1
====================

Released March, 2009.

3.8
   Care should be taken when adding functionality to essential and
   such additions create an obligation to support that functionality
   in essential forever unless significant work is done.

4.4
   Changelog files must be encoded in UTF-8.

4.4
   Some format requirements for changelog files are now "must" instead
   of "should."

4.4.1
   Alternative changelog formats have been removed. Debian only
   supports one changelog format for the Debian Archive.

4.9.1
   New nocheck option for DEB_BUILD_OPTIONS indicating any build-time
   test suite provided by the package should not be run.

5.1
   All control files must be encoded in UTF-8.

5.2
   "debian/control" allows comment lines starting with # with no
   preceding whitespace.

9.3
   Init scripts ending in .sh are not handled specially. They are not
   sourced and are not guaranteed to be run by "/bin/sh" regardless of
   the #! line. This brings Policy in line with the long-standing
   behavior of the init system in Debian.

9.3.2
   The start action of an init script must exit successfully and not
   start the daemon again if it's already running.

9.3.2
   "/var/run" and "/var/lock" may be mounted as temporary filesystems,
   and init scripts must therefore create any necessary subdirectories
   dynamically.

10.4
   "/bin/sh" scripts may assume that local can take multiple variable
   arguments and supports assignment.

11.6
   User mailboxes may be mode 600 and owned by the user rather than
   mode 660, owned by user, and group mail.


10.38. Version 3.8.0
====================

Released June, 2008.

2.4, 3.7
   The base section has been removed. contrib and non-free have been
   removed from the section list; they are only categories. The base
   system is now defined by priority.

4.9
   If "dpkg-source -x" doesn't provide the source that will be
   compiled, a debian/rules patch target is recommended and should do
   whatever else is necessary.

4.9.1, 10.1
   Standardized the format of DEB_BUILD_OPTIONS. Specified permitted
   characters for tags, required that tags be whitespace-separated,
   allowed packages to assume non-conflicting tags, and required
   unknown flags be ignored.

4.9.1
   Added parallel=n to the standardized DEB_BUILD_OPTIONS tags,
   indicating that a package should be built using up to n parallel
   processes if the package supports it

4.13
   Debian packages should not use convenience copies of code from
   other packages unless the included package is explicitly intended
   to be used that way.

4.14
   If dpkg-source -x doesn't produce source ready for editing and
   building with dpkg-buildpackage, packages should include a
   "debian/README.source" file explaining how to generate the patched
   source, add a new modification, and remove an existing
   modification. This file may also be used to document packaging a
   new upstream release and any other complexity of the Debian build
   process.

5.6.3
   The Uploaders field in debian/control may be wrapped.

5.6.12
   An empty Debian revision is equivalent to a Debian revision of 0 in
   a version number.

5.6.23
   New Homepage field for upstream web sites.

6.5, 6.6, 7
   The Breaks field declares that this package breaks another and
   prevents installation of the breaking package unless the package
   named in Breaks is deconfigured first. This field should not be
   used until the dpkg in Debian stable supports it.

8.1, 8.2
   Clarify which files should go into a shared library package, into a
   separate package, or into the -dev package. Suggest -tools instead
   of -runtime for runtime support programs, since that naming is more
   common in Debian.

9.5
   Files in "/etc/cron.{hourly,daily,weekly,monthly}" must be
   configuration files (upgraded from should). Mention the hourly
   directory.

11.8.6
   Packages providing "/etc/X11/Xresources" files need not conflict
   with "xbase (<< 3.3.2.3a-2)", which is long-obsolete.

12.1
   Manual pages in locale-specific directories should use either the
   legacy encoding for that directory or UTF-8. Country names should
   not be included in locale-specific manual page directories unless
   indicating a significant difference in the language. All characters
   in the manual page source should be representable in the legacy
   encoding for a locale even if the man page is encoded in UTF-8.

12.5
   The Apache 2.0 license is now in common-licenses and should be
   referenced rather than quoted in "debian/copyright".

12.5
   Packages in contrib and non-free should state in the copyright file
   that the package is not part of Debian GNU/Linux and briefly
   explain why.

debconf
   Underscore ("_") is allowed in debconf template names.


10.39. Version 3.7.3
====================

Released December, 2007.

5.6.12
   Package version numbers may contain tildes, which sort before
   anything, even the end of a part.

10.4
   Scripts may assume that "/bin/sh" supports local (at a basic level)
   and that its test builtin (if any) supports -a and -o binary
   logical operators.

8.5
   The substitution variable ${binary:Version} should be used in place
   of ${Source-Version} for dependencies between packages of the same
   library.

menu policy
   Substantial reorganization and renaming of sections in the Debian
   menu structure. Packages with menu entries should be reviewed to
   see if the menu section has been renamed or if one of the new
   sections would be more appropriate.

5.6.1
   The Source field in a ".changes" file may contain a version number
   in parentheses.

5.6.17
   The acceptable values for the Urgency field are low, medium, high,
   critical, or emergency.

8.6
   The shlibs file now allows an optional type field, indicating the
   type of package for which the line is valid. The only currently
   supported type is udeb, used with packages for the Debian
   Installer.

3.9.1
   Packages following the Debian Configuration management
   specification must allow for translation of their messages by using
   a gettext-based system such as po-debconf.

12.5
   GFDL 1.2, GPL 3, and LGPL 3 are now in common-licenses and should
   be referenced rather than quoted in debian/copyright.


10.40. Version 3.7.2.2
======================

Released October, 2006.

This release broke the normal rule against introducing normative
changes without changing the major patch level.

6.1
   Maintainer scripts must not be world writeable (up from a should to
   a must)


10.41. Version 3.7.2
====================

Released April, 2006.

11.5
   Revert the cgi-lib change.


10.42. Version 3.7.1
====================

Released April, 2006.

10.2
   It is now possible to create shared libraries without relocatable
   code (using -fPIC) in certain exceptional cases, provided some
   procedures are followed, and for creating static libraries with
   relocatable code (again, using -fPIC). Discussion on debian-
   devel@lists.debian.org, getting a rough consensus, and documenting
   it in README.Debian constitute most of the process.

11.8.7
   Packages should install any relevant files into the directories
   "/usr/include/X11/" and "/usr/lib/X11/", but if they do so, they
   must pre-depend on "x11-common (>= 1:7.0.0)"


10.43. Version 3.7.0
====================

Released April, 2006.

11.5
   Packages shipping web server CGI files are expected to install them
   in "/usr/lib/cgi-lib/" directories. This location change perhaps
   should be documented in NEWS

11.5
   Web server packages should include a standard scriptAlias of cgi-
   lib to "/usr/lib/cgi-lib".

9.1.1
   The version of FHS mandated by policy has been upped to 2.3. There
   should be no changes required for most packages, though new top
   level directories "/media", "/srv", etc. may be of interest.

5.1, 5.6.3
   All fields, apart from the Uploaders field, in the control file are
   supposed to be a single logical line, which may be spread over
   multiple physical lines (newline followed by space is elided).
   However, any parser for the control file must allow the Uploaders
   field to be spread over multiple physical lines as well, to prepare
   for future changes.

10.4
   When scripts are installed into a directory in the system PATH, the
   script name should not include an extension that denotes the
   scripting language currently used to implement it.

9.3.3.2
   packages that invoke initscripts now must use invoke-rc.d to do so
   since it also pays attention to run levels and other local
   constraints.

11.8.5.2, 11.8.7, etc
   We no longer use "/usr/X11R6", since we have migrated away to using
   Xorg paths. This means, for one thing, fonts live in
   "/usr/share/fonts/X11/" now, and "/usr/X11R6" is gone.


10.44. Version 3.6.2
====================

Released June, 2005.

   Recommend doc-base, and not menu, for registering package
   documentation.

8.1
   Run time support programs should live in subdirectories of
   "/usr/lib/" or "/usr/share", and preferably the shared lib is named
   the same as the package name (to avoid name collisions).

11.5
   It is recommended that HTTP servers provide an alias /images to
   allow packages to share image files with the web server


10.45. Version 3.6.1
====================

Released August, 2003.

3.10.1
   Prompting the user should be done using debconf. Non debconf user
   prompts are now deprecated.


10.46. Version 3.6.0
====================

Released July, 2003.

Restructuring caused shifts in section numbers and bumping of the
minor version number.

Many packaging manual appendices that were integrated into policy
sections are now empty, and replaced with links to the Policy. In
particular, the appendices that included the list of control fields
were updated (new fields like Closes, Changed-By were added) and the
list of fields for each of control, ".changes" and ".dsc" files is now
in Policy, and they're marked mandatory, recommended or optional based
on the current practice and the behavior of the deb-building tool-
chain.

Elimination of needlessly deep section levels, primarily in the
chapter Debian Archive, from which two new chapters were split out,
Binary packages and Source packages. What remained was reordered
properly, that is, some sects became sects etc.

Several sections that were redundant, crufty or simply not designed
with any sort of vision, were rearranged according to the formula that
everything should be either in the same place or properly interlinked.
Some things remained split up between different chapters when they
talked about different aspects of files: their content, their syntax,
and their placement in the file system. In particular, see the new
sections about changelog files.

menu policy
   Added Games/Simulation and Apps/Education to menu sub-policy

C.2.2
   Debian changelogs should be UTF-8 encoded.

10.2
   shared libraries must be linked against all libraries that they use
   symbols from in the same way that binaries are.

7.6
   build-depends-indep need not be satisfied during clean target.


10.47. Version 3.5.10
=====================

Released May, 2003.

11.8.3
   packages providing the x-terminal-emulator virtual package ought to
   ensure that they interpret the command line exactly like xterm
   does.

11.8.4
   Window managers compliant with the Window Manager Specification
   Project may add 40 points for ranking in the alternatives


10.48. Version 3.5.9
====================

Released March, 2003.

3.4.2
   The section describing the Description: package field once again
   has full details of the long description format.

4.2
   Clarified that if a package has non-build-essential build-
   dependencies, it should have them listed in the Build-Depends and
   related fields (i.e. it's not merely optional).

9.3.2
   When asked to restart a service that isn't already running, the
   init script should start the service.

12.6
   If the purpose of a package is to provide examples, then the
   example files can be installed into "/usr/share/doc/package"
   (rather than "/usr/share/doc/package/examples").


10.49. Version 3.5.8
====================

Released November, 2002.

12.7
   It is no longer necessary to keep a log of changes to the upstream
   sources in the copyright file. Instead, all such changes should be
   documented in the changelog file.

7.6
   Build-Depends, Build-Conflicts, Build-Depends-Indep, and Build-
   Conflicts-Indep must also be satisfied when the clean target is
   called.

menu policy
   A new Apps/Science menu section is available

debconf policy
   debconf specification cleared up, various changes.

12.1
   It is no longer recommended to create symlinks from nonexistent
   manual pages to *undocumented(7)*. Missing manual pages for
   programs are still a bug.


10.50. Version 3.5.7
====================

Released August, 2002.

   Packages no longer have to ask permission to call MAKEDEV in
   postinst, merely notifying the user ought to be enough.

2.2.4
   cryptographic software may now be included in the main archive.

3.9
   task packages are no longer permitted; tasks are now created by a
   special Tasks: field in the control file.

11.8.4
   window managers that support netwm can now add 20 points when they
   add themselves as an alternative for "/usr/bin/x-window-manager"

10.1
   The default compilation options have now changed, one should
   provide debugging symbols in all cases, and optionally step back
   optimization to -O0, depending on the DEB_BUILD_OPTIONS environment
   variable.

7.6, 4.8
   Added mention of build-arch, build-indep, etc, in describing the
   relationships with Build-Depends, Build-Conflicts, Build-Depends-
   Indep, and Build-Conflicts-Indep. May need to review the new rules.

8
   Changed rules on how, and when, to invoke ldconfig in maintainer
   scripts. Long rationale.

*Added the last note in 3.5.6 upgrading checklist item regarding build
rules, please see below*


10.51. Version 3.5.6
====================

Released July, 2001.

2.5
   Emacs and TeX are no longer mandated by policy to be priority
   standard packages

11.5
   Programs that access docs need to do so via "/usr/share/doc", and
   not via "/usr/doc/" as was the policy previously

12.3
   Putting documentation in "/usr/doc" versus "/usr/share/doc" is now
   a "serious" policy violation.

11.5
   For web servers, one should not provide non-local access to the
   "/usr/share/doc" hierarchy. If one can't provide access controls
   for the http://localhost/doc/ directory, then it is preferred that
   one ask permission to expose that information during the install.

7
   There are new rules for build-indep/build-arch targets and there is
   a new Build-Depend-Indep semantic.


10.52. Version 3.5.5
====================

Released May, 2001.

12.1
   Manpages should not rely on header information to have alternative
   manpage names available; it should only use symlinks or .so pages
   to do this

   *Clarified note in 3.5.3.0 upgrading checklist regarding examples
   and templates: this refers only to those examples used by scripts;
   see section 10.7.3 for the whole story*

   Included a new section 10.9.1 describing the use of dpkg-
   statoverride; this does not have the weight of policy

   Clarify Standards-Version: you don't need to rebuild your packages
   just to change the Standards-Version!

10.2
   Plugins are no longer bound by all the rules of shared libraries

X Windows related things:
   11.8.1
      Clarification of priority levels of X Window System related
      packages

   11.8.3
      Rules for defining x-terminal-emulator improved

   11.8.5
      X Font policy rewritten: you must read this if you provide fonts
      for the X Window System

   11.8.6
      Packages must not ship "/usr/X11R6/lib/X11/app-defaults/"

   11.8.7
      X-related packages should usually use the regular FHS locations;
      imake-using packages are exempted from this

   11.8.8
      OpenMotif linked binaries have the same rules as OSF/Motif-
      linked ones


10.53. Version 3.5.4
====================

Released April, 2001.

11.6
   The system-wide mail directory is now /var/mail, no longer
   /var/spool/mail. Any packages accessing the mail spool should
   access it via /var/mail and include a suitable Depends field;

11.9; perl-policy
   The perl policy is now part of Debian policy proper. Perl programs
   and modules should follow the current Perl policy


10.54. Version 3.5.3
====================

Released April, 2001.

7.1
   Build-Depends arch syntax has been changed to be less ambiguous.
   This should not affect any current packages

10.7.3
   Examples and templates files for use by scripts should now live in
   "/usr/share/<package>" or "/usr/lib/<package>", with symbolic links
   from "/usr/share/doc/<package>/examples" as needed


10.55. Version 3.5.2
====================

Released February, 2001.

11.8.6
   X app-defaults directory has moved from "/usr/X11R6/lib/X11/app-
   defaults" to "/etc/X11/app-defaults"


10.56. Version 3.5.1
====================

Released February, 2001.

8.1
   dpkg-shlibdeps now uses objdump, so shared libraries have to be run
   through dpkg-shlibdeps as well as executables


10.57. Version 3.5.0
====================

Released January, 2001.

11.8.5
   Font packages for the X Window System must now declare a dependency
   on "xutils (>= 4.0.2)"


10.58. Version 3.2.1.1
======================

Released January, 2001.

This release broke the normal rule against introducing normative
changes without changing the major patch level.

9.3.2
   Daemon startup scripts in "/etc/init.d/" should not contain
   modifiable parameters; these should be moved to a file in
   "/etc/default/"

12.3
   Files in "/usr/share/doc" must not be referenced by any program. If
   such files are needed, they must be placed in
   "/usr/share/<package>/", and symbolic links created as required in
   "/usr/share/doc/<package>/"

   Much of the packaging manual has now been imported into the policy
   document


10.59. Version 3.2.1
====================

Released August, 2000.

11.8.1
   A package of priority standard or higher may provide two binaries,
   one compiled with support for the X Window System, and the other
   without


10.60. Version 3.2.0
====================

Released August, 2000.

10.1
   By default executables should not be built with the debugging
   option -g. Instead, it is recommended to support building the
   package with debugging information optionally.

12.8
   Policy for packages where the upstream uses HTML changelog files
   has been expanded. In short, a plain text changelog file should
   always be generated for the upstream changes

   Please note that the new release of the X window system (3.2) shall
   probably need sweeping changes in policy

   Policy for packages providing the following X-based features has
   been codified:

   11.8.2
      X server (virtual package xserver)

   11.8.3
      X terminal emulator (virtual package x-terminal-emulator)

   11.8.4
      X window manager (virtual package x-window-manager, and
      "/usr/bin/x-window-manager" alternative, with priority
      calculation guidelines)

   12.8.5
      X fonts (this section has been written from scratch)

   11.8.6
      X application defaults

11.8.7
   Policy for packages using the X Window System and FHS issues has
   been clarified;

11.7.3
   No package may contain or make hard links to conffiles

8
   Noted that newer dpkg versions do not require extreme care in
   always creating the shared lib before the symlink, so the unpack
   order be correct


10.61. Version 3.1.1
====================

Released November, 1999.

7.1
   Correction to semantics of architecture lists in Build-Depends etc.
   Should not affect many packages


10.62. Version 3.1.0
====================

Released October, 1999.

defunct
   "/usr/doc/<package>" has to be a symlink pointing to
   "/usr/share/doc/<package>", to be maintained by postinst and prerm
   scripts.

7.1, 7.6
   Introduced source dependencies (Build-Depends, etc.)

9.3.4
   "/etc/rc.boot" has been deprecated in favour of "/etc/rcS.d".
   (Packages should not be touching this directory, but should use
   update-rc.d instead)

9.3.3
   update-rc.d is now the *only* allowable way of accessing the
   "/etc/rc?.d/[SK]??*" links. Any scripts which manipulate them
   directly must be changed to use update-rc.d instead. (This is
   because the file-rc package handles this information in an
   incompatible way.)

12.7
   Architecture-specific examples go in "/usr/lib/<package>/examples"
   with symlinks from "/usr/share/doc/<package>/examples/*" or from
   "/usr/share/doc/<package>/examples" itself

9.1.1
   Updated FHS to a 2.1 draft; this reverts "/var/state" to "/var/lib"

9.7; mime-policy
   Added MIME sub-policy document

12.4
   VISUAL is allowed as a (higher priority) alternative to EDITOR

11.6
   Modified liblockfile description, which affects mailbox-accessing
   programs. Please see the policy document for details

12.7
   If a package provides a changelog in HTML format, a text-only
   version should also be included. (Such a version may be prepared
   using "lynx -dump -nolist".)

3.2.1
   Description of how to handle version numbers based on dates added


10.63. Version 3.0.1
====================

Released July, 1999.

10.2
   Added the clarification that the .la files are essential for the
   packages using libtool's libltdl library, in which case the .la
   files must go in the run-time library package


10.64. Version 3.0.0
====================

Released June, 1999.

9.1
   Debian formally moves from the FSSTND to the FHS. This is a major
   change, and the implications of this move are probably not all
   known.

4.1
   Only 3 digits of the Standards version need be included in control
   files, though all four digits are still permitted.

12.6
   The location of the GPL has changed to "/usr/share/common-
   licenses". This may require changing the copyright files to point
   to the correct location of the GPL and other major licenses

10.2
   Packages that use libtool to create shared libraries must include
   the .la files in the -dev packages

10.8
   Use logrotate to rotate log files

now 11.8
   section 5.8 has been rewritten (Programs for the X Window System)

9.6; menu-policy
   There is now an associated menu policy, in a separate document,
   that carries the full weight of Debian policy

11.3
   Programs which need to modify the files "/var/run/utmp",
   "/var/log/wtmp" and "/var/log/lastlog" must be installed setgid
   utmp


10.65. Version 2.5.0
====================

Released October, 1998.

*Please note that section numbers below this point may not match the
current Policy Manual.*

* Rearranged the manual to create a new Section 4, Files

  * Section 3.3 ("Files") was moved to Section 4. The Sections that
    were Section 4 and Section 5 were moved down to become Section 5
    and Section 6.

  * What was Section 5.5 ("Log files") is now a subsection of the new
    Section 4 ("Files"), becoming section 4.8, placed after
    "Configuration files", moving the Section 4.8 ("Permissions and
    owners") to Section 4.9. All subsections of the old Section 5
    after 5.5 were moved down to fill in the number gap.

* Modified the section about changelog files to accommodate upstream
  changelogs which were formatted as HTML. These upstream changelog
  files should now be accessible as
  "/usr/doc/package/changelog.html.gz"

* Symlinks are permissible to link the real, or upstream, changelog
  name to the Debian mandated name.

* Clarified that HTML documentation should be present in some package,
  though not necessarily the main binary package.

* Corrected all references to the location of the copyright files. The
  correct location is "/usr/doc/package/copyright"

* Ratified the architecture specification strings to cater to the
  HURD.


10.66. Version 2.4.1
====================

Released April, 1998.

Updated section 3.3.5 Symbolic links
   symbolic links within a toplevel directory should be relative,
   symbolic links between toplevel directories should be absolute
   (cf., Policy Weekly Issue#6, topic 2)

Updated section 4.9 Games
   manpages for games should be installed in "/usr/man/man6" (cf.,
   Policy Weekly Issue#6, topic 3)

Updated Chapter 12 Shared Libraries
   ldconfig must be called in the postinst script if the package
   installs shared libraries (cf., Policy Weekly Issue #6,
   fixes:bug#20515)


10.67. Version 2.4.0
====================

Released January, 1998

Updated section 3.3.4 Scripts
   * /bin/sh may be any POSIX compatible shell

   * scripts including bashisms have to specify "/bin/bash" as
     interpreter

   * scripts which create files in world-writable directories (e.g.,
     in "/tmp") should use tempfile or mktemp for creating the
     directory

Updated section 3.3.5 Symbolic Links
   symbolic links referencing compressed files must have the same file
   extension as the referenced file

Updated section 3.3.6 Device files
   "/dev/tty*" serial devices should be used instead of "/dev/cu*"

Updated section 3.4.2 Writing the scripts in "/etc/init.d"
   * all "/etc/init.d" scripts have to provide the following options:
     start, stop, restart, force-reload

   * the reload option is optional and must never stop and restart the
     service

Updated section 3.5 Cron jobs
   cron jobs that need to be executed more often than daily should be
   installed into "/etc/cron.d"

Updated section 3.7 Menus
   removed section about how to register HTML docs to `menu' (the
   corresponding section in 4.4, Web servers and applications, has
   been removed in policy 2.2.0.0 already, so this one was obsolete)

New section 3.8 Keyboard configuration
   details about how the backspace and delete keys should be handled

New section 3.9 Environment variables
   no program must depend on environment variables to get a reasonable
   default configuration

New section 4.6 News system configuration
   "/etc/news/organization" and "/etc/news/server" should be supported
   by all news servers and clients

Updated section 4.7 Programs for the X Window System
   * programs requiring a non-free Motif library should be provided as
     foo-smotif and foo-dmotif package

   * if lesstif works reliably for such program, it should be linked
     against lesstif and not against a non-free Motif library

Updated section 4.9 Games
   games for X Windows have to be installed in "/usr/games", just as
   non-X games


10.68. Version 2.3.0
====================

Released September, 1997.

* new section `4.2 Daemons' including rules for "/etc/services",
  "/etc/protocols", "/etc/rpc", and "/etc/inetd.conf"

* updated section about `Configuration files': packages may not touch
  other packages' configuration files

* MUAs and MTAs have to use liblockfile


10.69. Version 2.2.0
====================

Released July, 1997.

* added section 4.1 `Architecture specification strings': use
  <arch>-linux where <arch> is one of the following: i386, alpha, arm,
  m68k, powerpc, sparc.

* detailed rules for "/usr/local"

* user ID's

* editor/pager policy

* cron jobs

* device files

* don't install shared libraries as executable

* app-defaults files may not be conffiles


10.70. Version 2.1.3
====================

Released March, 1997.

* two programs with different functionality must not have the same
  name

* "Webstandard 3.0"

* "Standard for Console Messages"

* Libraries should be compiled with "-D_REENTRANT"

* Libraries should be stripped with "strip --strip-unneeded"


10.71. Version 2.1.2
====================

Released November, 1996.

* Some changes WRT shared libraries


10.72. Version 2.1.1
====================

Released September, 1996.

* No hard links in source packages

* Do not use "dpkg-divert" or "update-alternatives" without
  consultation

* Shared libraries must be installed stripped


10.73. Version 2.1.0
====================

Released August, 1996.

* Upstream changelog must be installed too



11. License
***********

Copyright © 1996, 1997, 1998 Ian Jackson and Christian Schwarz

These are the copyright dates of the original Policy manual.  Since
then, this manual has been updated by many others.  No comprehensive
collection of copyright notices for subsequent work exists.

This manual is free software; you may redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.

This is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

A copy of the GNU General Public License is available as "/usr/share
/common-licenses/GPL" in the Debian distribution or on the World Wide
Web at https://www.gnu.org/licenses/.
