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# Installing From Source

If you are unable to use the binary wheels (for platforms where no pre-built wheels are available or if wheel installation is disabled), you can build gevent from source. A normal `pip install` will fallback to doing this if no binary wheel is available. (If you’ll be developing gevent, you’ll need to install from source also; follow that link for more details.)

## General Notes

- You can force installation of gevent from source with `pip install --no-binary gevent gevent`. This is useful if there is a binary wheel available, but you want to change the compile-time options, such as to use a system version of libuv instead of the embedded version. See Build-Time Configuration.

- You’ll need pip 19 and setuptools 40.8 with fully functional PEP 518 and PEP 517 support to install gevent from source.

- You’ll need a working C compiler toolchain that can build Python extensions. On some platforms, you may need to install Python development packages. You’ll also need the ability to compile cffi modules, which may require installing FFI development packages. Installing make and other common utilities such as file may also be required.

  For example, on Alpine Linux, one might need to do this:

      apk add --virtual build-deps file make gcc musl-dev libffi-dev

  On Fedora Rawhide for Fedora 33, one might need to do this:

      yum install python3-devel gcc kernel-devel kernel-headers make diffutils file

  (Newer versions of Fedora use `dnf` for package management but as of this writing `yum` is still available and widely used, especially for backwards compatibility.)

  On the Docker image for Ubuntu 20.04, one might need to do this:

      apt-get install python3.9-full python3.9-dev linux-headers-virtual make gcc libtool

  See issue #1567, issue #1559, and issue #1566.

  Note

  The exact set of external dependencies isn’t necessarily fixed and depends on the configure scripts of the bundled C libraries such as libev, libuv and c-ares. Disabling Embedding Libraries and using system libraries can reduce these dependencies, although this isn’t encouraged.

- On older versions of Linux, linking to `librt` might be useful to avoid system calls from libev accessing the current time. One way to do this is to set the `LDFLAGS` environment variable to include `-lrt` when installing from source. (This is done automatically when gevent builds manylinux wheels.) See pull request #1650.

- Installing from source requires `setuptools`. This is installed automatically in virtual environments and by buildout. However, gevent uses PEP 496 environment markers in `setup.py`. Consequently, you’ll need a version of setuptools newer than 25 (mid 2016) to install gevent from source; a version that’s too old will produce a `ValueError`. Older versions of pipenv may also have issues installing gevent for this reason.

- gevent 1.5 and newer come with a `pyproject.toml` file that installs the build dependencies, including CFFI (needed for libuv support). pip 18 or above is required for this support.

- You can use pip’s VCS support to install gevent directly from its code repository. This can be useful to check if a bug you’re experiencing has been fixed. For example, to install the current development version:

      pip install git+git://github.com/gevent/gevent.git#egg=gevent

  Often one would install this way into a virtual environment.

  If you’re using pip 18 or above, that should be all you need. If you have difficulties, see the development instructions for more information.

## Common Installation Issues

The following are some common installation problems and solutions for those compiling gevent from source.

- Some Linux distributions are now mounting their temporary directories with the `noexec` option. This can cause a standard `pip install gevent` to fail with an error like `cannot run C compiled programs`. One fix is to mount the temporary directory without that option. Another may be to use the `--build` option to `pip install` to specify another directory. See issue #570 and issue #612 for examples.

- Also check for conflicts with environment variables like `CFLAGS`. For example, see Library Updates.

- Users of a recent SmartOS release may need to customize the `CPPFLAGS` (the environment variable containing the default options for the C preprocessor) if they are using the libev shipped with gevent. See Operating Systems for more information.

- If you see `ValueError: ("Expected ',' or end-of-list in", "cffi >= 1.11.5 ; sys_platform == 'win32' and platform_python_implementation == 'CPython'", 'at', " ; sys_platform == 'win32' and platform_python_implementation == 'CPython'")`, the version of setuptools is too old. Install a more recent version of setuptools.

## Build-Time Configuration

There are a few knobs that can be tweaked at gevent build time. These are mostly useful for downstream packagers. They all take the form of environment variables that must be set when `setup.py` is called (note that `pip install` will invoke `setup.py`). Toggle flags that have boolean values may take the form of 0/1, true/false, off/on, yes/no.

`CPPFLAGS`

  A standard variable used when building the C extensions. gevent may make slight modifications to this variable.

  An important symbol is `NDEBUG`. Unless this is defined, C-level assertions are enabled. libev and libuv are very aggressive about their assertions, and some of their choices do not fit the way gevent is intended to be used. It’s best to make sure this is defined, e.g., `CPPFLAGS=-DNDEBUG`.

`CFLAGS`

  A standard variable used when building the C extensions. gevent may make slight modifications to this variable.

`LDFLAGS`

  A standard variable used when building the C extensions. gevent may make slight modifications to this variable.

`GEVENTSETUP_EV_VERIFY`

  If set, the value is passed through as the value of the `EV_VERIFY` C compiler macro when libev is embedded. This should be an integer between 0 and 3; values larger than 1 are likely to cause problems with gevent applications. Also if set, this makes sure that the `NDEBUG` preprocessor symbol isn’t defined so that the C `assert` function works (failed assertions crash the process).

  Important

  This note is for downstream packagers, such as Linux distributions. Please do not distribute gevent built with this setting enabled, as it is only for development and testing, not production usage.

  In general, setting `CPPFLAGS` is more general and can contain other macros recognized by libev.

### Embedding Libraries

By default, gevent builds and embeds tested versions of its C dependencies libev, libuv, and c-ares. This is the recommended configuration as the specific versions used are tested by gevent, and sometimes require patches to be applied. Moreover, embedding, especially in the case of libev, can be more efficient as features not needed by gevent can be disabled, resulting in smaller or faster libraries or runtimes.

However, this can be disabled, either for all libraries at once or for individual libraries.

Important

This is not a suggested or recommended configuration. It can break gevent in unexpected ways, and usually carries a performance cost. Downstream packagers are strongly encouraged to allow gevent to use its embedded libraries.

When embedding a library is disabled, the library must already be installed on the system in a way the compiler can access and link (i.e., correct `CPPFLAGS`, etc) in order to use the corresponding C extension.

`GEVENTSETUP_EMBED`

  A boolean defaulting to true. When turned off (e.g., `GEVENTSETUP_EMBED=0`), libraries are not embedded in the gevent C extensions. The value of this is used as the default for all the libraries if no more specific version is defined.

`GEVENTSETUP_EMBED_LIBEV`

  Controls embedding libev.

`GEVENTSETUP_EMBED_CARES`

  Controls embedding c-ares.

`GEVENTSETUP_EMBED_LIBUV`

  This is not defined or used, only a CFFI extension is available and those are always embedded.

Older versions of gevent supported `EMBED` and `LIBEV_EMBED`, etc, to mean the same thing. Those aliases still work but are deprecated and print a warning.