The CGI (Common Gateway Interface) defines a way for a web server to interact with external content-generating programs, which are often referred to as CGI programs or CGI scripts.

Within Tomcat, CGI support can be added when you are using Tomcat as your HTTP server and require CGI support. Typically this is done during development when you don't want to run a web server like Apache httpd. Tomcat's CGI support is largely compatible with Apache httpd's, but there are some limitations (e.g., only one cgi-bin directory).

CGI support is implemented using the servlet class org.apache.catalina.servlets.CGIServlet. Traditionally, this servlet is mapped to the URL pattern "/cgi-bin/*".

By default CGI support is disabled in Tomcat.

CAUTION - CGI scripts are used to execute programs external to the Tomcat JVM. If you are using the Java SecurityManager this will bypass your security policy configuration in catalina.policy.

Remove the XML comments from around the CGI servlet and servlet-mapping configuration in $CATALINA_BASE/conf/web.xml.

Only Contexts which are marked as privileged may use the CGI servlet (see the privileged property of the Context element).

There are several servlet init parameters which can be used to configure the behaviour of the CGI servlet.

• cgiPathPrefix - The CGI search path will start at the web application root directory + File.separator + this prefix. The default cgiPathPrefix is WEB-INF/cgi
• debug - Debugging detail level for messages logged by this servlet. Default 0.
• executable - The of the executable to be used to run the script. Default is perl.
• envHttpHeaders - A regular expression used to select the HTTP headers passed to the CGI process as environment variables. Note that headers are converted to upper case before matching and that the entire header name must match the pattern. Default is ACCEPT[-0-9A-Z]*|CACHE-CONTROL|COOKIE|HOST|IF-[-0-9A-Z]*|REFERER|USER-AGENT
• parameterEncoding - Name of the parameter encoding to be used with the GCI servlet. Default is System.getProperty("file.encoding","UTF-8").
• passShellEnvironment - Should the shell environment variables (if any) be passed to the CGI script? Default is false.
• stderrTimeout - The time (in milliseconds) to wait for the reading of stderr to complete before terminating the CGI process. Default is 2000.