### 30.2 The NSS Configuration File ¶

Somehow the NSS code must be told about the wishes of the user. For this reason there is the file `/etc/nsswitch.conf`. For each database, this file contains a specification of how the lookup process should work. The file could look like this:

    # /etc/nsswitch.conf
    #
    # Name Service Switch configuration file.
    #

    passwd:     db files
    shadow:     files
    group:      db files

    hosts:      files dns
    networks:   files

    ethers:     db files
    protocols:  db files
    rpc:        db files
    services:   db files

The first column is the database as you can guess from the table above. The rest of the line specifies how the lookup process works. Please note that you specify the way it works for each database individually. This cannot be done with the old way of a monolithic implementation.

The configuration specification for each database can contain two different items:

- the service specification like `files`, `db`, or `nis`.
- the reaction on lookup result like `[NOTFOUND=return]`.