Apache HTTP Server Version 2.2
Apache Module mod_cgi
| Description: | Execution of CGI scripts |
|---|---|
| Status: | Base |
| Module Identifier: | cgi_module |
| Source File: | mod_cgi.c |
Summary
Any file that has the handler
cgi-script will be treated
as a CGI script, and run by the server, with its output being
returned to the client. Files acquire this handler either by
having a name containing an extension defined by the
AddHandler directive, or by being
in a ScriptAlias
directory.
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.
For backward-compatibility, the cgi-script handler will also be activated
for any file with the mime-type application/x-httpd-cgi. The
use of the magic mime-type is deprecated.
See also
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
AcceptPathInfodirective is explicitly set tooff. The default behavior, ifAcceptPathInfois not given, is thatmod_cgiwill accept path info (trailing/more/path/infofollowing the script filename in the URI), while the core server will return a 404 NOT FOUND error for requests with additional path info. Omitting theAcceptPathInfodirective has the same effect as setting itOnformod_cgirequests. - REMOTE_HOST
- This will only be set if
HostnameLookupsis set toon(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
IdentityCheckis set toonand 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.
This module also leverages the core functions ap_add_common_vars and ap_add_cgi_vars to add environment variables like:
- DOCUMENT_ROOT
- Set with the content of the related
DocumentRootdirective. - SERVER_NAME
- The fully qualified domain name related to the request.
- SERVER_ADDR
- The IP address of the Virtual Host serving the request.
- SERVER_ADMIN
- Set with the content of the related
ServerAdmindirective.
For an exhaustive list it is suggested to write a basic CGI script that dumps all the environment variables passed by Apache in a convenient format.
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.
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:
%%error
error-message
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).
ScriptLog Directive
| 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
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.
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.
ScriptLogBuffer Directive
| 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.
ScriptLogLength Directive
| Description: | Size limit of the CGI script logfile |
|---|---|
| Syntax: | ScriptLogLength bytes |
| Default: | ScriptLogLength 10385760 |
| Context: | server config, virtual host |
| Status: | Base |
| Module: | mod_cgi, mod_cgid |
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.