This page documents the 1.4 (latest stable) release. Documentation for other releases can be found here.

Trac and mod_python

Trac supports ​mod_python, which speeds up Trac's response times considerably, especially compared to TracCgi, and permits use of many Apache features not possible with tracd/mod_proxy.

Attention: These instructions apply to Trac version 0.9. If you're installing Trac 0.8.x, please see a ​previous version of this page. If you're upgrading from 0.8.x to 0.9, please read the upgrade instructions.

Be sure to grab mod_python 3.1.3 and later for SetHandler mod_python directive to work. Also, older versions may generate an internal error (see #1090)

What is the preferred MPM method, or does it matter (worker or prefork)

Simple configuration

If you just installed mod_python, you may have to add a line to load the module in the Apache configuration:

LoadModule python_module modules/mod_python.so
Note: On FreeBSD 6.1 and Apache 2.2.x use LoadModule python_module libexec/apache22/mod_python.so

A simple setup of Trac on mod_python looks like this:

<Location /projects/myproject>
   SetHandler mod_python
   PythonHandler trac.web.modpython_frontend 
   PythonOption TracEnv /var/trac/myproject
   PythonOption TracUriRoot /projects/myproject
</Location>

Notes:

1. The option TracUriRoot may or may not be necessary in your setup. Try your configuration with out it, and if the URLs produced by Trac look wrong or if Trac does not seem to recognize the URLs correctly, add the TracUriRoot option. You will notice that the Location and TracUriRoot have the same path.
2. Your web server may need the ability to write to files in the TracEnv directory on your server. You can change these by using the chown utility on *nix based servers. You may see an error similar to this in your http error log if this is the case:

"TracError: The user root requires read _and_ write permission to the database file /home/svn/project/db/trac.db and the directory it is located in."

3. You can test your mod_python installation by adding the following to your httpd.conf. You should remove this when you are done testing for security reasons.

      <Location /mpinfo>
         SetHandler mod_python
         PythonHandler mod_python.testhandler
      </Location>
   

Configuring Authentication

Configuring authentication works the same as for CGI:

<Location "/projects/myproject/login">
  AuthType Basic
  AuthName "myproject"
  AuthUserFile /var/trac/myproject/.htpasswd
  Require valid-user
</Location>

Configuring PythonPath

If the Trac installation isn't installed in your Python path, you'll have to tell Apache where to find the Trac mod_python handler using the PythonPath directive:

<Location /projects/myproject>
  ...
  PythonPath "sys.path + ['/path/to/trac']"
  ...
</Location>

Note that if you're using Subversion, you will often have to add the path to the Subversion bindings there, as the bindings are often found outside of the site-packages area (e.g. could be /opt/subversion-1.3.0/lib/svn-python).

Be also careful about really using the PythonPath directive, and not SetEnv PYTHONPATH, as the latter won't work.

Setting up multiple projects

The Trac mod_python handler supports a configuration option similar to Subversion's SvnParentPath, called TracEnvParentDir:

<Location /projects>
  SetHandler mod_python
  PythonHandler trac.web.modpython_frontend 
  PythonOption TracEnvParentDir /var/trac
  PythonOption TracUriRoot /projects
</Location>

When you request the /projects URL, you will get a listing of all subdirectories of the directory you set as TracEnvParentDir. Selecting any project in the list will bring you to the corresponding Trac environment.

If you don't want to have the subdirectory listing as your projects home page you can use a

<LocationMatch "/.+/">

This will instruct Apache to use mod_python for all locations different from root while having the possibility of placing a custom home page for root in your DocumentRoot folder.

You can also use the same authentication realm for all of the projects using a <LocationMatch> directive:

<LocationMatch "/projects/[^/]+/login">
  AuthType Basic
  AuthName "Trac"
  AuthUserFile /var/trac/.htpasswd
  Require valid-user
</LocationMatch>

Virtual Host Configuration

Below is the sample configuration required to set up your trac as a virtual server (i.e. when you access it at the URLs like http://trac.mycompany.com):

<VirtualHost * >
    DocumentRoot /var/trac/myproject
    ServerName trac.mycompany.com
    <Location />
        SetHandler mod_python
        PythonHandler trac.web.modpython_frontend
        PythonOption TracEnv /var/trac/myproject
        PythonOption TracUriRoot /
    </Location>
    <Location /login>
        AuthType Basic
        AuthName "MyCompany Trac Server"
        AuthUserFile /var/trac/myproject/.htpasswd
        Require valid-user
    </Location>
</VirtualHost>

If your images and CSS are not applying properly add this within the VirtualHost directives

    Alias /trac /usr/share/trac/htdocs
    <LocationMatch /trac/>
        SetHandler None
    </LocationMatch>

For a virtual host that supports multiple projects replace "TracEnv" /var/trac/myproject with "TracEnvParentDir" /var/trac/

Troubleshooting

'Server Error' Page Displayed

Assuming you are confident that mod_python is installed and working properly (An example of a simple test setup can be found here: ​http://www.dscpl.com.au/articles/modpython-001.html), if you get the following error in your browser:

The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there was an error in a CGI script.

1. And you get the following entries in your Apache error log:

...File "/usr/lib64/python2.3/site-packages/mod_python/apache.py", line 287, in HandlerDispatch\n    log=debug)
...PythonHandler trac.web.modpython_frontend:   File "/usr/lib64/python2.3/site-packages/mod_python/apache.py", line 454, in import_module\n    f, p, d = imp.find_module(parts[i], path)

... PythonHandler trac.web.modpython_frontend: ImportError: No module named trac 

Make sure the 'trac' directory that was created during installation has the appropriate permissions in order for the user your web server runs under to 'see' the files contained in it. This directory will be in the 'site-packages' directory of your platform's installation. A 'chmod -R 755 ./trac' resolved the issue for me. Modify as necessary for your security preferences.

2. And you get the following entries in your Apache error log:

...
...PythonHandler trac.web.modpython_frontend:   File "/lib/python2.4/site-packages/trac/db.py", line 211, in _rollback_on_error\n    return function(self, *args, **kwargs)
...PythonHandler trac.web.modpython_frontend: OperationalError: unsupported file format

It's probably due to that you have a mod_php module in apache with SQLite support compiled into it. Unless one configures mod_php with "—without-sqlite" it will be compiled with PHP's internal SQLite-support, which is SQLite 2.x. This will confuse apache when Trac, and mod_python, dynamically tries to load another version of the SQLite library. Most probably the same version the SQLite database is constructed by, why the SQLite 2.x version included in mod_php gives the above error. Solution is either to unload mod_php or to compile mod_php without sqlite-support.

Form submission problems

If you're experiencing problems submitting some of the forms in Trac (a common problem is that you get redirected to the start page after submission), check whether your DocumentRoot contains a folder or file with the same path that you mapped the mod_python handler to. For some reason, mod_python gets confused when it is mapped to a location that also matches a static resource.

Problem with VHost configuration

If the <Location /> directive is used, DocumentRoot setting leads to an 403 (FORBIDDEN) error. Log message: "client is forbidden by server configuration". Without the DocumentRoot it just works fine.

Using .htaccess

Although it may seem trivial to rewrite the above configuration as a directory in your document root with a .htaccess file, this does not work. Apache will append a "/" to any Trac URLs, which interferes with its correct operation.

It may be possible to work around this with mod_rewrite, but I failed to get this working. In all, it is more hassle than it is worth. Stick to the provided instructions. :)

Win32 Issues

Don't feel like compiling the source? Windows installers are available at the following URLs. Make sure you grab an installer which works with your version of Python: ​http://www.apache.org/dist/httpd/modpython/win/3.2.7/ or ​http://www.lehuen.com/nicolas/download/mod_python/

If you run trac with mod_python < 3.2 on Windows, uploading attachments will not work. This problem which is discussed in #554 is resolved in mod_python > 3.1.4 so please upgrade mod_python to fix this.

OS X issues

When using mod_python on OS X you will not be able to restart Apache using apachectl restart. This is apparently fixed in mod_python 3.2, but there's also a patch available for earlier versions ​here.

SELinux issues

If Trac reports something like: Cannot get shared lock on db.lock The security context on the repository may need to be set:

chcon -R -h -t httpd_sys_content_t PATH_TO_REPOSITORY

See also ​http://subversion.tigris.org/faq.html#reposperms

FreeBSD issues

Pay attention to the version of installed mod_python and sqlite. Ports have both the new and old ones, but earlier versions of pysqlite and mod_python won't integrate as first require threaded support in python, and the second require threadless.

Also, seems like in FreeBSD some environment(maybe ldconfig) update is required right after installation of trac for trac-admin actually started working. I've missed the exact requirement, but noticed that immediately after installation trac-admin refused to do initenv, but after I relogged in to different shell - all worked perfectly.

Subversion issues

If you get the following Trac Error Unsupported version control system "svn" only under mod_python, though it works well on the command-line and even with TracStandalone, chances are that you forgot to add the path to the Python bindings with the PythonPath directive.

If this is not the case, it's possible that you're using Subversion libraries that are binary incompatible with the apache ones (an incompatibility of the apr libraries is usually the cause). In that case, you also won't be able to use the svn modules for Apache (mod_dav_svn).

Using /trac root URL

If you wish your trac to be at ​http://example.com/trac, the default config will not display images or CSS correctly, and the config must be changed.

/chrome is configurable (and infact needs to be changed) in /var/trac/myproject/conf/trac.ini

[trac]
...
htdocs_location = /trac/chrome/

Then in the VirtualHost directives

    Alias /trac/chrome /usr/share/trac/htdocs
    <LocationMatch /trac/chrome/>
        SetHandler None
    </LocationMatch>

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See also TracGuide, TracInstall, TracCgi, TracFastCgi, TracMultipleProjectsSVNAccess