Edgewall Software

Trac and Apache suEXEC

Trac in CGI-mode doesn't play very well with Apache suEXEC. The suEXEC feature provides users of the Apache HTTP Server the ability to run CGI and SSI programs under user IDs different from the user ID of the calling web server. Normally, when a CGI or SSI program executes, it runs as the same user who is running the web server.

Setting the TRAC_ENV environment variable as described in TracInstall will not work when using suEXEC feature, because the environment variables are filtered and only a limited subset reaches the CGI program.

There are obvious workarounds to make things work:

  1. Recompile suexec to let it pass the TRAC_ENV variable; this requires root permissions and therefore not advisable.
  2. Change our trac.cgi script to set the TRAC_ENV variable by itself, to do this we edit trac.cgi file and add to the start of the script:
    import os
    os.environ['TRAC_ENV'] = '/path/to/projectenv'
  3. Make a wrapper script:
    export TRAC_ENV='/path/to/projectenv'
    exec /path/to/trac/trac.cgi

Note: This is a kludge, but works.

Multiple Projects under suEXEC

When hosting multiple projects under suEXEC, you can either copy the CGI script and change the TRAC_ENV setting for each script, or make a wrapper script around it. Here is a script to work around the stripping of environment variables done by suEXEC:


export TRAC_ENV="/home/${user}/.trac/prj/${prj}" 
export SCRIPT_NAME="/~${user}/prj/${prj}" 
export PATH_INFO="${PATH_INFO#/${prj}}" 
export PYTHONPATH="/home/${user}/sw/lib/python2.3/site-packages" 
exec ./trac.cgi 

Multiple Projects under Plesk/suEXEC/same domain

Added by torgny at sbbs.se

The above script works well if you want to have a Trac instance for each user, but it doesn't really help if you have several projects under the same site, SourceForge style. In order to solve this under Linux Red Hat with Plesk, I did the following:

First, from the Apache configuration (vhost.conf in this case), replace DOMAIN with the domain you are adding:

RewriteEngine on
RewriteRule ^/projects/+$                                    /projects/index.php  [L]
RewriteCond /home/httpd/vhosts/DOMAIN/private/tracs/$1  -d
RewriteRule ^/projects/([^/]+)(/?.*)                         /projects/wrap.cgi$2 [S=1,E=TRAC_ENV:/home/httpd/vhosts/DOMAIN/private/tracs/$1]
RewriteRule ^/projects/(.*)                                  /projects/index.php

Alias /trac/ /usr/share/trac/htdocs/

<Directory "/usr/share/trac/htdocs">
    Options Indexes MultiViews
    AllowOverride None
    Order allow,deny
    Allow from all

<Directory "/home/httpd/vhosts/DOMAIN/httpdocs/projects">
    AllowOverride None
    Options ExecCGI -MultiViews +SymLinksIfOwnerMatch
    AddHandler cgi-script .cgi
    Order allow,deny
    Allow from all

<LocationMatch "/projects/[[:alnum:]]+/login">
    AuthType Basic
    AuthName "Trac"
    AuthUserFile /home/httpd/vhosts/DOMAIN/private/.htpasswd_trac
    Require valid-user

Now add the folder ~/httpdocs/projects.

In that folder, either symlink trac.cgi or place a copy, and add index.php. index.php acts as the default page when a project without an existing Trac environment is requested.

Now, for the wrap.cgi bash script:

export TRAC_ENV="/home/httpd/vhosts/${DOMAIN}/private/tracs/${project}"
export SCRIPT_NAME="/projects/${project}"
exec ./trac.cgi

The script above does all the work-around magic to make sure everything works between suEXEC and Trac in CGI mode. It also gives you multiple projects support.

Multiple Projects, suExec, and RHEL 4

Added by mjs at clemson.edu

Here are some points specific to a RHEL installation.

My layout is as follows:

  • Project Trac installations are in /home/tracker/Trac/Projects/project-a, /home/tracker/Trac/Projects/project-b, etc.
  • The Trac site is a separate vhost from our other Web pages.
  • The Trac site lives in /home/tracker/Trac/htdocs/.
  • /home/tracker/Trac/cgi-bin is a symlink to /var/www/cgi-bin/tracker/ (see below).
  • URLs are http://trac.example.com/projects/project-a, etc.

Red Hat compiles suExec so that it only executes CGI scripts that live below /var/www. You cannot symlink individual scripts, but you can symlink a directory. This means that we can't drop CGI scripts under doc root. The scripts will have to live in the cgi-bin subdirectory. Scripts must also not be group-writable.

The Trac vhost is defined as follows:

<VirtualHost *:80>
    ServerAdmin webmaster@example.com
    DocumentRoot /home/tracker/Trac/htdocs
    ServerName trac.example.com

    RewriteEngine on
    RewriteRule ^/projects/+$               /projects/index.html  [L]
    RewriteCond /home/tracker/Trac/Projects/$1  -d
    RewriteRule ^/projects/([^/]+)(/?.*)    /cgi-bin/tracwrap.cgi$2 [S=1,PT]
    RewriteRule ^/projects/(.*)             /projects/index.html

    ScriptAlias /cgi-bin/ "/home/tracker/Trac/cgi-bin/"
    SuexecUserGroup tracker tracker
    ErrorLog /var/log/trac/error_log
    CustomLog /var/log/trac/access_log combined
    Alias /icons /home/tracker/Trac/htdocs/icons


  • The ScriptAlias line enables CGI script invocation in the named subdirectory. This subdirectory must be a symlink to a directory under /var/www/cgi-bin.
  • The second RewriteRule finds the project name and appends anything following it to the rewritten URL. Normally, the result of a RewriteRule is appended to the path to doc root. The PT ("Pass Through") flag prevents this, so /cgi-bin/tracwrap.cgi is invoked as a script.
  • The E flag in torgny's example is superfluous, as suExec strips it from the environment anyway.

As above, the tracwrap.cgi script sets environment variables for trac.cgi depending on the project name:

export TRAC_ENV="/home/tracker/Trac/Projects/${project}"
export SCRIPT_NAME="/projects/${project}"
exec ./trac.cgi

I found that the variables you need to manipulate are quite different than in torgny's example. SCRIPT_URL contains the entire local URL, e.g., "/projects/project-a/login" and PATH_INFO already contains anything after the project name. So to get the project name, you need to strip "/project/" off the front of ${SCRIPT_URL} and "${PATH_INFO}" off the end. On entry, SCRIPT_NAME contains "tracwrap.cgi", not anything related to the project name.

See also: TracInstall, TracMultipleProjects

Last modified 8 years ago Last modified on Feb 21, 2015, 1:08:31 PM
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