Since version 0.9, Trac supports ?plugins that extend the built-in functionality. The plugin functionality is based on the ?component architecture.
Plugins can be either installed globally, in a shared plugins directory (see Global Configuration) or locally for specific TracEnvironment, in its plugins directory. Except for the later case, the components defined in a plugin should be explicitly enabled in the [components] section of the trac.ini file.
To use egg based plugins in Trac, you need to have ?setuptools (version 0.6) installed.
To install setuptools, download the bootstrap module ?ez_setup.py and execute it as follows:
$ python ez_setup.py
If the ez_setup.py script fails to install the setuptools release, you can download it from ?PyPI and install it manually.
Plugins can also consist of a single .py file dropped into either the environment or the shared plugins directory.
Plugins are packaged as ?Python eggs. That means they are ZIP archives with the file extension .egg.
If you have downloaded a source distribution of a plugin, and want to build the .egg file, follow this instruction:
$ python setup.py bdist_egg
Then you will have a *.egg file. Examine the output of running python to find where this was created.
Once you have the plugin archive, you need to copy it into the plugins directory of the project environment. Also, make sure that the web server has sufficient permissions to read the plugin egg. Then, restart the web server (this requirement was not previously mentioned in this document, but in my tests it began working only after I did so).
To uninstall a plugin installed this way, remove the egg from plugins directory and restart web server.
Note that the Python version that the egg is built with must match the Python version with which Trac is run. If for instance you are running Trac under Python 2.5, but have upgraded your standalone Python to 2.6, the eggs won't be recognized.
Note also that in a multi-project setup, a pool of Python interpreter instances will be dynamically allocated to projects based on need, and since plugins occupy a place in Python's module system, the first version of any given plugin to be loaded will be used for all the projects. In other words, you cannot use different versions of a single plugin in two projects of a multi-project setup. It may be safer to install plugins for all projects (see below) and then enable them selectively on a project-by-project basis.
Some plugins (such as ?SpamFilter) are downloadable as a .egg file which can be installed with the easy_install program:
If easy_install is not on your system see the Requirements section above to install it. Windows users will need to add the Scripts directory of their Python installation (for example, C:\Python24\Scripts) to their PATH environment variable (see ?easy_install Windows notes for more information).
If Trac reports permission errors after installing a zipped egg and you would rather not bother providing a egg cache directory writable by the web server, you can get around it by simply unzipping the egg. Just pass --always-unzip to easy_install:
easy_install --always-unzip TracSpamFilter-0.2.1dev_r5943-py2.4.egg
You should end up with a directory having the same name as the zipped egg (complete with .egg extension) and containing its uncompressed contents.
Trac also searches for plugins installed in the shared plugins directory (since 0.10), see TracIni#GlobalConfiguration. This is a convenient way to share the installation of plugins across several but not all environments.
easy_install makes installing from source a snap. Just give it the URL to either a Subversion repository or a tarball/zip of the source:
Unlike plugins installed per-environment, you'll have to explicitly enable globally installed plugins via trac.ini. This also applies to plugins installed in shared plugins directory, i.e. the path specified in the [inherit] plugins_dir configuration option.
This is done in the [components] section of the configuration file, for example:
[components] tracspamfilter.* = enabled
The name of the option is the Python package of the plugin. This should be specified in the documentation of the plugin, but can also be easily discovered by looking at the source (look for a top-level directory that contains a file named __init__.py.)
Note: After installing the plugin, you need to restart your web server.
easy_install or python setup.py does not have an uninstall feature. Hower, it is usually quite trivial to remove a globally installed egg and reference:
If you are uncertain about the location of the egg, here is a small tip to help locate an egg (or any package) - replace myplugin with whatever namespace the plugin uses (as used when enabling the plugin):
>>> import myplugin >>> print myplugin.__file__ /opt/local/python24/lib/site-packages/myplugin-0.4.2-py2.4.egg/myplugin/__init__.pyc
Some plugins will need to be extracted by the Python eggs runtime (pkg_resources), so that their contents are actual files on the file system. The directory in which they are extracted defaults to '.python-eggs' in the home directory of the current user, which may or may not be a problem. You can however override the default location using the PYTHON_EGG_CACHE environment variable.
To do this from the Apache configuration, use the SetEnv directive as follows:
SetEnv PYTHON_EGG_CACHE /path/to/dir
This works whether you are using the CGI or the mod_python front-end. Put this directive next to where you set the path to the Trac environment, i.e. in the same <Location> block.
For example (for CGI):
<Location /trac> SetEnv TRAC_ENV /path/to/projenv SetEnv PYTHON_EGG_CACHE /path/to/dir </Location>
or (for mod_python):
<Location /trac> SetHandler mod_python ... SetEnv PYTHON_EGG_CACHE /path/to/dir </Location>
Note: SetEnv requires the mod_env module which needs to be activated for Apache. In this case the SetEnv directive can also be used in the mod_python Location block.
For FastCGI, you'll need to -initial-env option, or whatever is provided by your web server for setting environment variables.
Note: that if you already use -initial-env to set the project directory for either a single project or parent you will need to add an additional -initial-env directive to the FastCgiConfig directive. I.e.
FastCgiConfig -initial-env TRAC_ENV=/var/lib/trac -initial-env PYTHON_EGG_CACHE=/var/lib/trac/plugin-cache
If you have set up some subversion hook scripts that call the Trac engine - such as the post-commit hook script provided in the /contrib directory - make sure you define the PYTHON_EGG_CACHE environment variable within these scripts as well.
Try this from the command line:
$ python -c "import pkg_resources"
If you get no output, setuptools is installed. Otherwise, you'll need to install it before plugins will work in Trac.
Python eggs have the Python version encoded in their filename. For example, MyPlugin-1.0-py2.5.egg is an egg for Python 2.5, and will not be loaded if you're running a different Python version (such as 2.4 or 2.6).
Also, verify that the egg file you downloaded is indeed a ZIP archive. If you downloaded it from a Trac site, chances are you downloaded the HTML preview page instead.
If you install a plugin globally (i.e. not inside the plugins directory of the Trac project environment) you will have to explicitly enable it in trac.ini. Make sure that:
Trac must be able to read the file.
Enable logging and set the log level to DEBUG, then watch the log file for messages about loading plugins.
Some plugins require you have special permissions in order to use them. ?WebAdmin, for example, requires the user to have TRAC_ADMIN permissions for it to show up on the navigation bar.
If you put your plugins inside plugins directories, and certainly if you have more than one project, you need to make sure that the correct version of the plugin is loading. Here are some basic rules:
OK, so the logs don't mention plugins, the egg is readable, the python version is correct and the egg has been installed globally (and is enabled in the trac.ini) and it still doesn't work or give any error messages or any other indication as to why? Hop on the ?IrcChannel and ask away.
See also TracGuide, ?plugin list, ?component architecture