Apache Module mod_cgi

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Description:	Execution of CGI scripts
Status:	Base
Module Identifier:	cgi_module
Source File:	mod_cgi.c

Summary

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Any file that has the mime type - application/x-httpd-cgi or handler - cgi-script (Apache 1.1 or later) will be treated - as a CGI script, and run by the server, with its output being - returned to the client. Files acquire this type either by - having a name containing an extension defined by the - AddType directive, or by being - in a ScriptAlias - directory.

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When the server invokes a CGI script, it will add a variable - called DOCUMENT_ROOT to the environment. This - variable will contain the value of the - DocumentRoot configuration - variable.

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For an introduction to using CGI scripts with Apache, see - our tutorial on Dynamic Content - With CGI.

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When using a multi-threaded MPM under unix, the module - mod_cgid should be used in place of - this module. At the user level, the two modules are essentially - identical.

Topics

CGI Environment variables
CGI Debugging

CGI Environment variables

The server will set the CGI environment variables as described - in the CGI - specification, with the following provisions:

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PATH_INFO: This will not be available if the AcceptPathInfo directive is explicitly set to - off. The default behavior, if AcceptPathInfo is not given, is that mod_cgi will accept path info (trailing - /more/path/info following the script filename in the URI), - while the core server will return a 404 NOT FOUND error for requests - with additional path info. Omitting the AcceptPathInfo directive has the same effect as setting - it On for mod_cgi requests.
REMOTE_HOST: This will only be set if HostnameLookups is set to on (it - is off by default), and if a reverse DNS lookup of the accessing - host's address indeed finds a host name.
REMOTE_IDENT: This will only be set if IdentityCheck is set to - on and the accessing host supports the ident - protocol. Note that the contents of this variable cannot be - relied upon because it can easily be faked, and if there is a - proxy between the client and the server, it is usually - totally useless.
REMOTE_USER: This will only be set if the CGI script is subject to - authentication.

CGI Debugging

Debugging CGI scripts has traditionally been difficult, mainly - because it has not been possible to study the output (standard - output and error) for scripts which are failing to run - properly. These directives, included in Apache 1.2 and later, - provide more detailed logging of errors when they occur.

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CGI Logfile Format

When configured, the CGI error log logs any CGI which does not - execute properly. Each CGI script which fails to operate causes - several lines of information to be logged. The first two lines - are always of the format:

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- %% [time] request-line - %% HTTP-status CGI-script-filename -

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If the error is that CGI script cannot be run, the log file - will contain an extra two lines:

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- %%error - error-message -

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Alternatively, if the error is the result of the script - returning incorrect header information (often due to a bug in - the script), the following information is logged:

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- %request - All HTTP request headers received - POST or PUT entity (if any) - %response - All headers output by the CGI script - %stdout - CGI standard output - %stderr - CGI standard error -

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(The %stdout and %stderr parts may be missing if the script did - not output anything on standard output or standard error).

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ScriptLog Directive

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Description:	Location of the CGI script error logfile
Syntax:	`ScriptLog file-path`
Context:	server config, virtual host
Status:	Base
Module:	`mod_cgi`, `mod_cgid`

The ScriptLog directive sets the CGI - script error logfile. If no ScriptLog is given, - no error log is created. If given, any CGI errors are logged into the - filename given as argument. If this is a relative file or path it is - taken relative to the ServerRoot. -

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Example

- ScriptLog logs/cgi_log -

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This log will be opened as the user the child processes run - as, i.e. the user specified in the main User directive. This means that - either the directory the script log is in needs to be writable - by that user or the file needs to be manually created and set - to be writable by that user. If you place the script log in - your main logs directory, do NOT change the - directory permissions to make it writable by the user the child - processes run as.

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Note that script logging is meant to be a debugging feature - when writing CGI scripts, and is not meant to be activated - continuously on running servers. It is not optimized for speed - or efficiency, and may have security problems if used in a - manner other than that for which it was designed.

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ScriptLogBuffer Directive

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Description:	Maximum amount of PUT or POST requests that will be recorded -in the scriptlog
Syntax:	`ScriptLogBuffer bytes`
Default:	`ScriptLogBuffer 1024`
Context:	server config, virtual host
Status:	Base
Module:	`mod_cgi`, `mod_cgid`

The size of any PUT or POST entity body that is logged to - the file is limited, to prevent the log file growing too big - too quickly if large bodies are being received. By default, up - to 1024 bytes are logged, but this can be changed with this - directive.

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ScriptLogLength Directive