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.

+ +

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:

+ +

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. +

+ +

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