Quick Installation Guide

This document describes the steps for installing mod_wsgi on a UNIX system from the original source code.

Apache Requirements

Apache 2.0, 2.2 or 2.4 can be used.

For Apache 2.0, 2.2 and 2.4, the single threaded ‘prefork’ or multithreaded ‘worker’ Apache MPMs can be used. For Apache 2.4 the ‘event’ MPM can also be used.

The version of Apache and its runtime libraries must have be compiled with support for threading.

On Linux systems, if Apache has been installed from a package repository, you must have installed the corresponding Apache “dev” package as well.

For most Linux distributions, the “dev” package for Apache 2.X is “apache2-dev” where the corresponding Apache package was “apache2”. Some systems however distinguish the “dev” package based on which MPM is used by Apache. As such, it may also be called “apache2-worker-dev” or “apache2-prefork-dev”. If using Apache 2.X, do not mix things up and install “apache-dev” by mistake, which is the “dev” package for Apache 1.3 called just “apache”.

Python Requirements

Any Python 2.X version from Python 2.6 onwards can be used. For Python 3.X, you will need Python 3.3 or later.

The version of Python being used must have been compiled with support for threading.

On Linux systems, if Python has been installed from a package repository, you must have installed the corresponding Python “dev” package as well.

Python should preferably be available as a shared library. If this is not the case then base runtime memory usage of mod_wsgi will be greater.

Unpacking The Source Code

Source code tar balls can be obtained from:

After having downloaded the tar ball for the version you want to use, unpack it with the command:

tar xvfz mod_wsgi-X.Y.tar.gz

Replace ‘X.Y’ with the actual version number for that being used.

Configuring The Source Code

To setup the package ready for building run the “configure” script from within the source code directory:

./configure

The configure script will attempt to identify the Apache installation to use by searching in various standard locations for the Apache build tools included with your distribution called “apxs2” or “apxs”. If not found in any of these standard locations, your PATH will be searched.

Which Python installation to use will be determined by looking for the “python” executable in your PATH.

If these programs are not in a standard location, they cannot be found in your PATH, or you wish to use alternate versions to those found, the --with-apxs and --with-python options can be used in conjunction with the “configure” script:

./configure --with-apxs=/usr/local/apache/bin/apxs \
  --with-python=/usr/local/bin/python

On some Linux distributions, such as SUSE and CentOS, it will be necessary to use the --with-apxs option and specify either “/usr/sbin/apxs2-worker” or “/usr/sbin/apxs2-prefork”. This is necessary as the Linux distribtions allow installation of “dev” packages for both Apache MPM variants at the same time, whereas other Linux distributions do not.

If you have multiple versions of Python installed and you are not using that which is the default, you may have to organise that the PATH inherited by the Apache application when run will result in Apache finding the alternate version. Alternatively, the WSGIPythonHome directive should be used to specify the exact location of the Python installation corresponding to the version of Python compiled against. If this is not done, the version of Python running within Apache may attempt to use the Python modules from the wrong version of Python.

Building The Source Code

Once the package has been configured, it can be built by running:

make

If the mod_wsgi source code does not build successfully, see:

If successful, the only product of the build process that needs to be installed is the Apache module itself. There are no separate Python code files as everything is done within C code compiled into the Apache module.

To install the Apache module into the standard location for Apache modules as dictated by Apache for your installation, run:

make install

Installation should be done as the ‘root’ user or ‘sudo’ command if appropriate.

If you want to install the Apache module in a non standard location dictated by how your operating system distribution structures the configuration files and modules for Apache, you will need to copy the file manually into place.

If installing the Apache module by hand, the file is called ‘mod_wsgi.so’. The compiled Apache module can be found in the ”.libs” subdirectory. The name of the file should be kept the same when copied into its appropriate location.

Loading Module Into Apache

Once the Apache module has been installed into your Apache installation’s module directory, it is still necessary to configure Apache to actually load the module.

Exactly how this is done and in which of the main Apache configuration files it should be placed, is dependent on which version of Apache you are using and may also be influenced by how your operating system’s Apache distribution has organised the Apache configuration files. You may therefore need to check with any documentation for your operating system to see in what way the procedure may need to be modified.

In the simplest case, all that is required is to add a line of the form:

LoadModule wsgi_module modules/mod_wsgi.so

into the main Apache “httpd.conf” configuration file at the same point that other Apache modules are being loaded. The last option to the directive should either be an absolute path to where the mod_wsgi module file is located, or a path expressed relative to the root of your Apache installation. If you used “make” to install the package, see where it copied the file to work out what to set this value to.

Restart Apache Web Server

Having adding the required directives you should perform a restart of Apache to check everything is okay. If you are using an unmodified Apache distribution from the Apache Software Foundation, a restart is performed using the ‘apachectl’ command:

apachectl restart

If you see any sort of problem, or if you are upgrading from an older version of mod_wsgi, it is recommended you actually stop and the start Apache instead:

apachectl stop
apachectl start

Note that on many Linux distributions where Apache is prepackaged, the Apache software has been modified and as a result the ‘apachectl’ command may not work properly or the command may not be present. On these systems, you will need to use whatever is the sanctioned method for restarting system services.

This may be via an ‘init.d’ script:

/etc/init.d/httpd stop
/etc/init.d/httpd start

or via some special service maintenance script.

On Debian derived distributions, restarting Apache is usually done via the ‘invoke-rc.d’ command:

invoke-rc.d apache2 stop
invoke-rc.d apache2 start

On RedHat derived distributions, restarting Apache is usually done via the ‘service’ command:

service httpd stop
service httpd start

In nearly all cases the scripts used to restart Apache will need to be run as the ‘root’ user or via ‘sudo’.

In general, for any system where you are using a prepackaged version of Apache, it is wise to always check the documentation for that package or system to determine the correct way to restart the Apache service. This is because they often use a wrapper around ‘apachectl’, or replace it, with a script which performs additional actions.

If all is okay, you should see a line of the form:

Apache/2.4.8 (Unix) mod_wsgi/4.4.21 Python/2.7 configured

in the Apache error log file.

Cleaning Up After Build

To cleanup after installation, run:

make clean

If you need to build the module for a different version of Apache, you should run:

make distclean

and then rerun “configure” against the alternate version of Apache before attempting to run “make” again.