Apache module mod_cgi
This module provides for execution of CGI scripts.
Source File: mod_cgi.c
Module Identifier: cgi_module
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. Files that are not in a ScriptAlias directory, but which are of type
application/x-httpd-cgi by virtue of an
AddType directive, will still not be executed by the server unless
Options ExecCGI is enabled. See the
Options directive for more details.
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.
For an introduction to using CGI scripts with Apache, see our tutorial on Dynamic Content with CGI.
See also: Options, ScriptAlias, AddType and AddHandler.
CGI Environment variables
The server will set the CGI environment variables as described in the CGI specification, with the following provisions: 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.
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.
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:
%% [time] request-line %% HTTP-status CGI-script-filename
If the error is that CGI script cannot be run, the log file will contain an extra two lines:
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:
%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
(The %stdout and %stderr parts may be missing if the script did not output anything on standard output or standard error).
Syntax: ScriptLog filename
Context: server config
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 server root.
This log will be opened as the user the child processes run as, ie. 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.
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.
Syntax: ScriptLogLength bytes
Context: server config
ScriptLogLength can be used to limit the size of the CGI script logfile. Since the logfile logs a lot of information per CGI error (all request headers, all script output) it can grow to be a big file. To prevent problems due to unbounded growth, this directive can be used to set an maximum file-size for the CGI logfile. If the file exceeds this size, no more information will be written to it.
Syntax: ScriptLogBuffer bytes
Context: server config
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.
Apache HTTP Server Version 1.3