ImportError: No module named trac.web.modpython_frontend

One of the reasons why you might get the error:

ImportError: No module named trac.web.modpython_frontend

after installing Trac is because of the fact that apache may not be able to create the Python egg cache, which is detailed in the Trac wiki right here. This will also generate the above error if not set up correctly. Create a directory for the files, change the owner to www-data.www-data (or something else, depending on which user you run Trac under) and rejoice.

The settings needed in the vhost configuration (.. or wherever you have your configuration ..):

        SetHandler mod_python
        PythonInterpreter main_interpreter
        PythonHandler trac.web.modpython_frontend
        PythonOption TracEnvParentDir /path/to/trac
        PythonOption TracUriRoot /
        PythonOption PYTHON_EGG_CACHE /path/to/directory/you/created

You can easily do a quick test by setting the path to /tmp and checking if that solved your problem. If it did, create a dedicated directory and live happily ever after. If it didn’t, continue your quest. Check for genshi and other dependencies. Do a search on Google ™.

Hopefully everything works again.

BTW: Another reason for this error might be that your trac installation may no longer be available (if your installation uses a version number in the library path and you upgraded the python version, this path will change – and your old libraries may not have been copied over), so it might help reinstalling Trac in your new environment:

easy_install -U Trac

.. and then try again (thanks to Christer for reporting on this after he had the same problem).

Post-commit hook failed with error output: .. and nothing more.

While getting the trac-svn integration up and running in one of our repositories tonight, I stumbled across this issue. Most links I found on Google said to try to run the post-commit script by itself under the same user, which worked just fine. Checked that all my paths were absolute paths to avoid assuming any CWD, but still nothing. After trying to minimize the problem I discovered that even with a post-commit-script of just environmental assignments, things were still failing. This nabble archived thread did however give a very important hint by Ryan Schmidt (who obviously has solved the post-commit problems for every single developer out there, if I were to judge by the number of times his name comes up. Awesome work, Ryan.):

Your post-commit must also begin with a line like “#!/bin/sh” and have its executable bit set.

Wow. Homer Simpson “Doh!”-moment right there. No #!/bin/bash (or #!/bin/sh) ment that SVN weren’t able to run the script with the proper interpreter. When running it from the command line, bash were already running of course, so it just assumed that it was a bash script .. and it were right.

Thanks Ryan, saved me a couple of hours tonight.