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# Changes between Version 3 and Version 4 of TracModPython

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Jul 17, 2018, 3:10:47 PM (23 months ago)
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 v3 = Trac and mod_python = [[TracGuideToc]] = Trac and mod_python Mod_python is an [https://httpd.apache.org/ Apache] module that embeds the Python interpreter within the server, so that web-based applications in Python will run many times faster than traditional CGI and will have the ability to retain database connections. Trac supports [http://www.modpython.org/ mod_python], which speeds up Trac's response times considerably, especially compared to [TracCgi CGI], and permits use of many Apache features not possible with [wiki:TracStandalone tracd]/mod_proxy. {{{#!div class="important" ** A Word of Warning ** As of 16^th^ June 2010, the mod_python project is officially dead.  If you are considering using mod_python for a new installation, '''please don't'''!  There are known issues which will not be fixed and there are now better alternatives.  Check out the main TracInstall pages for your target version for more information. }}} These instructions are for Apache 2; if you are still using Apache 1.3, you may have some luck with [trac:wiki:TracModPython2.7 TracModPython2.7], but you'll be totally on your own. [[PageOutline(2-3,Overview,inline)]] == Simple configuration: single project == #Simpleconfiguration == Simple configuration: single project #Simpleconfiguration If you just installed mod_python, you may have to add a line to load the module in the Apache configuration: {{{ {{{#!apache LoadModule python_module modules/mod_python.so }}} ''Note: The exact path to the module depends on how the HTTPD installation is laid out.'' On Debian using apt-get {{{ '''Note''': The exact path to the module depends on how the HTTPD installation is laid out. On Debian using apt-get: {{{#!sh apt-get install libapache2-mod-python libapache2-mod-python-doc }}} (Still on Debian) after you have installed mod_python, you must enable the modules in apache2 (equivalent of the above Load Module directive): {{{ Still on Debian, after you have installed mod_python, you must enable the modules in apache2, equivalent to the above Load Module directive: {{{#!sh a2enmod python }}} On Fedora use, using yum: {{{ {{{#!sh yum install mod_python }}} 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. Note: mod_python.testhandler is only available in mod_python 3.2+. {{{ #!xml 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. Note: mod_python.testhandler is only available in mod_python 3.2+. {{{#!apache SetHandler mod_python PythonInterpreter main_interpreter PythonHandler mod_python.testhandler Order allow,deny Allow from all SetHandler mod_python PythonInterpreter main_interpreter PythonHandler mod_python.testhandler # For Apache 2.2 Order allow,deny Allow from all # For Apache 2.4 Require all granted }}} A simple setup of Trac on mod_python looks like this: {{{ #!xml {{{#!apache SetHandler mod_python PythonInterpreter main_interpreter PythonHandler trac.web.modpython_frontend PythonOption TracEnv /var/trac/myproject PythonOption TracUriRoot /projects/myproject Order allow,deny Allow from all }}} The option '''TracUriRoot''' may or may not be necessary in your setup. Try your configuration without it; if the URLs produced by Trac look wrong, if Trac does not seem to recognize URLs correctly, or you get an odd "No handler matched request to..." error, add the '''TracUriRoot''' option.  You will notice that the Location and '''TracUriRoot''' have the same path. The options available are {{{ # For a single project PythonOption TracEnv /var/trac/myproject # For multiple projects PythonOption TracEnvParentDir /var/trac/myprojects # For the index of multiple projects PythonOption TracEnvIndexTemplate /srv/www/htdocs/trac/project_list_template.html # A space delimitted list, with a "," between key and value pairs. PythonOption TracTemplateVars key1,val1 key2,val2 # Useful to get the date in the wanted order PythonOption TracLocale en_GB.UTF8 # See description above PythonOption TracUriRoot /projects/myproject }}} === Python Egg Cache === Compressed python eggs like Genshi are normally extracted into a directory named .python-eggs in the users home directory. Since apache's home usually is not writable an alternate egg cache directory can be specified like this: {{{ SetHandler mod_python PythonInterpreter main_interpreter PythonHandler trac.web.modpython_frontend PythonOption TracEnv /var/trac/myproject PythonOption TracUriRoot /projects/myproject # For Apache 2.2 Order allow,deny Allow from all # For Apache 2.4 Require all granted }}} The option '''TracUriRoot''' may or may not be necessary in your setup. Try your configuration without it; if the URLs produced by Trac look wrong, if Trac does not seem to recognize URLs correctly, or you get an odd "No handler matched request to..." error, add the '''TracUriRoot''' option. You will notice that the Location and '''TracUriRoot''' have the same path. The options available are: {{{#!apache # For a single project PythonOption TracEnv /var/trac/myproject # For multiple projects PythonOption TracEnvParentDir /var/trac/myprojects # For the index of multiple projects PythonOption TracEnvIndexTemplate /srv/www/htdocs/trac/project_list_template.html # A space delimitted list, with a "," between key and value pairs. PythonOption TracTemplateVars key1,val1 key2,val2 # Useful to get the date in the wanted order PythonOption TracLocale en_GB.UTF8 # See description above PythonOption TracUriRoot /projects/myproject }}} === Python Egg Cache Compressed Python eggs like Genshi are normally extracted into a directory named .python-eggs in the users home directory. Since Apache's home usually is not writeable, an alternate egg cache directory can be specified like this: {{{#!apache PythonOption PYTHON_EGG_CACHE /var/trac/myprojects/egg-cache }}} or you can uncompress the Genshi egg to resolve problems extracting from it. === Configuring Authentication === Or you can uncompress the Genshi egg to resolve problems extracting from it. === Configuring Authentication See corresponding section in the [wiki:TracModWSGI#ConfiguringAuthentication] page. == Advanced Configuration === Setting the Python Egg Cache === If the Egg Cache isn't writeable by your Web server, you'll either have to change the permissions, or point Python to a location where Apache can write. This can manifest itself as a ''500 internal server error'' and/or a complaint in the syslog. {{{ #!xml === Setting the Python Egg Cache If the Egg Cache isn't writeable by your Web server, you'll either have to change the permissions, or point Python to a location where Apache can write. This can manifest itself as a 500 internal server error and/or a complaint in the syslog. {{{#!apache ... }}} === Setting the !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: {{{ #!xml === Setting the !PythonPath If the Trac installation isn't installed in your Python path, you will have to tell Apache where to find the Trac mod_python handler  using the PythonPath directive: {{{#!apache ... Be careful about using the !PythonPath directive, and ''not'' SetEnv PYTHONPATH, as the latter won't work. === Setting up multiple projects === === Setting up multiple projects The Trac mod_python handler supports a configuration option similar to Subversion's SvnParentPath, called TracEnvParentDir: {{{ #!xml {{{#!apache SetHandler mod_python If you don't want to have the subdirectory listing as your projects home page you can use a {{{ #!xml {{{#!apache }}} You can also use the same authentication realm for all of the projects using a  directive: {{{ #!xml {{{#!apache AuthType Basic }}} === 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): {{{ #!xml === Virtual Host Configuration Below is the sample configuration required to set up your Trac as a virtual server, ie when you access it at the URLs like http://trac.mycompany.com: {{{#!apache DocumentRoot /var/www/myproject ServerName trac.mycompany.com This does not seem to work in all cases. What you can do if it does not: * Try using  instead of  * may, in your server setup, refer to the complete host instead of simple the root of the server. This means that everything (including the login directory referenced below) will be sent to python and authentication does not work (i.e. you get the infamous Authentication information missing error). If this applies to you, try using a sub-directory for trac instead of the root (i.e. /web/ and /web/login instead of / and /login). * Try using  instead of . *  may, in your server setup, refer to the complete host instead of simple the root of the server. This means that everything (including the login directory referenced below) will be sent to Python and authentication does not work, ie you get the infamous Authentication information missing error. If this is the case, try using a sub-directory for Trac instead of the root, ie /web/ and /web/login instead of / and /login. * Depending on apache's NameVirtualHost configuration, you may need to use  instead of . For a virtual host that supports multiple projects replace "TracEnv" /var/trac/myproject with "TracEnvParentDir" /var/trac/ Note: !DocumentRoot should not point to your Trac project env. As Asmodai wrote on #trac: "suppose there's a webserver bug that allows disclosure of !DocumentRoot they could then leech the entire Trac environment". == Troubleshooting == In general, if you get server error pages, you can either check the Apache error log, or enable the PythonDebug option: {{{ #!xml For a virtual host that supports multiple projects replace TracEnv /var/trac/myproject with TracEnvParentDir /var/trac. '''Note''': !DocumentRoot should not point to your Trac project env. As Asmodai wrote on #trac: "suppose there's a webserver bug that allows disclosure of !DocumentRoot they could then leech the entire Trac environment". == Troubleshooting If you get server error pages, you can either check the Apache error log, or enable the PythonDebug option: {{{#!apache ... For multiple projects, try restarting the server as well. === Login Not Working === === Login Not Working If you've used  directive, it will override any other directives, as well as . The workaround is to use negation expression as follows (for multi project setups): {{{ #!xml {{{#!apache #this one for other pages PythonOption TracEnvParentDir /projects PythonOption TracUriRoot / #this one for login page This problem will most certainly hit you on Unix when using Python 2.4. In Python 2.4, some version of Expat (an XML parser library written in C) is used, and if Apache is using another version, this results in segmentation faults. As Trac 0.11 is using Genshi, which will indirectly use Expat, that problem can now hit you even if everything was working fine before with Trac 0.10. See Graham Dumpleton's detailed [http://www.dscpl.com.au/wiki/ModPython/Articles/ExpatCausingApacheCrash explanation and workarounds] for the issue. === Form submission problems === In Python 2.4, some version of [http://expat.sourceforge.net/ Expat] (an XML parser library written in C) is used and if Apache is using another version, this results in segmentation faults. As Trac 0.11 is using Genshi, which will indirectly use Expat, that problem can now hit you even if everything was working fine before with Trac 0.10. This problem has not been reported for Python 2.5+, so best to upgrade. === 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 virtual host configuration === If the directive is used, setting the DocumentRoot may result in a ''403 (Forbidden)'' error. Either remove the DocumentRoot directive, or make sure that accessing the directory it points is allowed (in a corresponding  block). Using together with SetHandler resulted in having everything handled by mod_python, which leads to not being able download any CSS or images/icons. I used SetHandler None to circumvent the problem, though I do not know if this is the most elegant solution. === Problem with zipped egg === It's possible that your version of mod_python will not import modules from zipped eggs. If you encounter an ImportError: No module named trac in your Apache logs but you think everything is where it should be, this might be your problem. Look in your site-packages directory; if the Trac module appears as a ''file'' rather than a ''directory'', then this might be your problem. To rectify, try installing Trac using the --always-unzip option, like this: {{{ === Problem with virtual host configuration If the directive is used, setting the DocumentRoot may result in a ''403 (Forbidden)'' error. Either remove the DocumentRoot directive, or make sure that accessing the directory it points is allowed, in a corresponding  block. Using together with SetHandler resulted in having everything handled by mod_python, which leads to not being able to download any CSS or images/icons. Use SetHandler None to circumvent the problem, though this may not be the most elegant solution. === Problem with zipped egg It's possible that your version of mod_python will not import modules from zipped eggs. If you encounter an ImportError: No module named trac in your Apache logs but you think everything is where it should be, this might be your problem. Look in your site-packages directory; if the Trac module appears as a ''file'' rather than a ''directory'', then this might be your problem. To rectify this, try installing Trac using the --always-unzip option: {{{#!sh easy_install --always-unzip Trac-0.12b1.zip }}} === Using .htaccess === === 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. :) A success story: For me it worked out-of-box, with following trivial config: {{{#!xml 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. This also works out-of-box, with following trivial config: {{{#!apache SetHandler mod_python PythonInterpreter main_interpreter }}} The TracUriRoot is obviously the path you need to enter to the browser to get to the trac (e.g. domain.tld/projects/trac) === Additional .htaccess help === If you are using the .htaccess method you may have additional problems if your trac directory is inheriting .htaccess directives from another. This may also help to add to your .htaccess file: {{{ The TracUriRoot is obviously the path you need to enter to the browser to get to Trac, eg domain.tld/projects/trac. === Additional .htaccess help If you are using the .htaccess method you may have additional problems if your Trac directory is inheriting .htaccess directives from another. This may also help to add to your .htaccess file: {{{#!apache RewriteEngine Off === Platform specific issues ==== Win32 Issues ==== If you run trac with mod_python < 3.2 on Windows, uploading attachments will '''not''' work. This problem is resolved in mod_python 3.1.4 or later, 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 [http://www.dscpl.com.au/projects/vampire/patches.html 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: {{{ ==== Win32 Issues If you run Trac with mod_python < 3.2 on Windows, uploading attachments will '''not''' work. This problem is resolved in mod_python 3.1.4 or later, 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, so please upgrade mod_python to fix this. ==== SELinux issues If Trac reports something like: Cannot get shared lock on db.lock, then the security context on the repository may need to be set: {{{#!sh 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 the installed mod_python and sqlite packages. Ports have both the new and old ones, but earlier versions of pysqlite and mod_python won't integrate as the former requires threaded support in python, and the latter requires a threadless install. If you compiled and installed apache2, apache wouldn´t support threads (cause it doesn´t work very well on FreeBSD). You could force thread support when running ./configure for apache, using --enable-threads, but this isn´t recommendable. The best option [http://modpython.org/pipermail/mod_python/2006-September/021983.html seems to be] adding to /usr/local/apache2/bin/ennvars the line {{{ See also [http://subversion.apache.org/faq.html#reposperms How do I set repository permissions correctly?] ==== FreeBSD issues The FreeBSD ports have both the new and old versions of mod_python and SQLite, but earlier versions of pysqlite and mod_python won't integrate: * pysqlite requires threaded support in Python * mod_python requires a threadless install. Apache2 does not automatically support threads on FreeBSD. You could force thread support when running ./configure for Apache, using --enable-threads, but this isn´t recommended. The best option [http://modpython.org/pipermail/mod_python/2006-September/021983.html seems to be] adding to /usr/local/apache2/bin/ennvars the line: {{{#!sh export LD_PRELOAD=/usr/lib/libc_r.so }}} ==== Fedora 7 Issues ==== Make sure you install the 'python-sqlite2' package as it seems to be required for TracModPython but not for tracd === 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 [TracModPython#ConfiguringPythonPath PythonPath] directive. (The better way is to add a link to the bindings in the Python site-packages directory, or create a .pth file in that directory.) 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). You also need a recent version of mod_python in order to avoid a runtime error ({{{argument number 2: a 'apr_pool_t *' is expected}}}) due to the default usage of multiple sub-interpreters. 3.2.8 ''should'' work, though it's probably better to use the workaround described in [trac:#3371 #3371], in order to force the use of the main interpreter: {{{ ==== Fedora 7 Issues Make sure you install the 'python-sqlite2' package as it seems to be required for TracModPython, but not for tracd. === 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 [TracModPython#ConfiguringPythonPath PythonPath] directive. A better way is to add a link to the bindings in the Python site-packages directory, or create a .pth file in that directory. If this is not the case, it's possible that you are using Subversion libraries that are binary incompatible with the Apache ones and 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). You also need a recent version of mod_python in order to avoid a runtime error ({{{argument number 2: a 'apr_pool_t *' is expected}}}) due to the default usage of multiple sub-interpreters. Version 3.2.8 ''should'' work, though it's probably better to use the workaround described in [trac:#3371 #3371], in order to force the use of the main interpreter: {{{#!apache PythonInterpreter main_interpreter }}} This is anyway the recommended workaround for other well-known issues seen when using the Python bindings for Subversion within mod_python ([trac:#2611 #2611], [trac:#3455 #3455]). See in particular Graham Dumpleton's comment in [trac:comment:9:ticket:3455 #3455] explaining the issue. === Page layout issues === If the formatting of the Trac pages look weird chances are that the style sheets governing the page layout are not handled properly by the web server. Try adding the following lines to your apache configuration: {{{ #!xml This is also the recommended workaround for other issues seen when using the Python bindings for Subversion within mod_python ([trac:#2611 #2611], [trac:#3455 #3455]). See in particular Graham Dumpleton's comment in [trac:comment:9:ticket:3455 #3455] explaining the issue. === Page layout issues If the formatting of the Trac pages look weird, chances are that the style sheets governing the page layout are not handled properly by the web server. Try adding the following lines to your Apache configuration: {{{#!apache Alias /myproject/css "/usr/share/trac/htdocs/css" }}} Note: For the above configuration to have any effect it must be put after the configuration of your project root location, i.e. {{{}}}. Also, setting PythonOptimize On seems to mess up the page headers and footers, in addition to hiding the documentation for macros and plugins (see #Trac8956). Considering how little effect the option has, it is probably a good idea to leave it Off. === HTTPS issues === If you want to run Trac fully under https you might find that it tries to redirect to plain http. In this case just add the following line to your apache configuration: {{{ #!xml '''Note''': For the above configuration to have any effect it must be put after the configuration of your project root location, ie {{{}}}. **Note:** Do not enable python optimizations using the directive PythonOptimize On. When optimizations are enabled the page header/footer and documentation for macros and plugins will be hidden. An error will be raised in Trac 1.0.11 and later when optimizations are enabled. === HTTPS issues If you want to run Trac fully under https you might find that it tries to redirect to plain http. In this case just add the following line to your Apache configuration: {{{#!apache DocumentRoot /var/www/myproject ServerName trac.mycompany.com }}} === Segmentation fault with php5-mhash or other php5 modules === You may encounter segfaults (reported on debian etch) if php5-mhash module is installed. Try to remove it to see if this solves the problem. See debian bug report [http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=411487] Some people also have troubles when using php5 compiled with its own 3rd party libraries instead of system libraries. Check here [http://www.djangoproject.com/documentation/modpython/#if-you-get-a-segmentation-fault] === Segmentation fault with php5-mhash or other php5 modules You may encounter segfaults (reported on Debian etch) if php5-mhash module is installed. Try to remove it to see if this solves the problem. See [http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=411487 Debian bug report]. Some people also have troubles when using PHP5 compiled with its own third party libraries instead of system libraries. Check [http://www.djangoproject.com/documentation/modpython/#if-you-get-a-segmentation-fault Django segmentation fault]. ---- See also:  TracGuide, TracInstall, [wiki:TracModWSGI ModWSGI], [wiki:TracFastCgi FastCGI],  [trac:TracNginxRecipe TracNginxRecipe] See also: TracGuide, TracInstall, [wiki:TracModWSGI ModWSGI], [wiki:TracFastCgi FastCGI], [trac:TracNginxRecipe]