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  Apache HTTP Server Version 1.3
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<H1 ALIGN="CENTER">Module mod_cgi</H1>

This module is contained in the <CODE>mod_cgi.c</CODE> file, and
is compiled in by default. It provides for execution of CGI scripts.
Any file with mime type <CODE>application/x-httpd-cgi</CODE> will be
processed by this module.
<!--%plaintext &lt;?INDEX {\tt application/x-httpd-cgi} mime type&gt; -->
<!--%plaintext &lt;?INDEX CGI scripts&gt; -->

<H2>Summary</H2>
Any file that has the mime type <CODE>application/x-httpd-cgi</CODE>
or handler <CODE>cgi-script</CODE> (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
<A HREF="mod_mime.html#addtype">AddType</A> directive, or by being in
a <A HREF="mod_alias.html#scriptalias">ScriptAlias</A> directory. <P>

When the server invokes a CGI script, it will add a variable called
<CODE>DOCUMENT_ROOT</CODE> to the environment. This variable will contain the
value of the <A HREF="core.html#documentroot">DocumentRoot</A>
configuration variable.

<H2>CGI Environment variables</H2>
The server will set the CGI environment variables as described in the
<A HREF="http://hoohoo.ncsa.uiuc.edu/cgi/">CGI specification</A>, with the
following provisions:
<DL>
<DT>REMOTE_HOST
<DD>This will only be set if <A HREF="core.html#hostnamelookups"><CODE>HostnameLookups</CODE></A>
is set to <CODE>on</CODE> (it is off by default), and if a reverse DNS
lookup of the accessing host's address indeed finds a host name.
<DT>REMOTE_IDENT
<DD>This will only be set if
<A HREF="core.html#identitycheck">IdentityCheck</A> is set to <CODE>on</CODE>
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.
<DT>REMOTE_USER
<DD>This will only be set if the CGI script is subject to authentication.
</DL>
<P>

<HR>

<H2><A NAME="cgi_debug">CGI Debugging</A></H2>

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.

<HR>

<H2>CGI Logfile Format</H2>

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:

<PRE>
  %% [<EM>time</EM>] <EM>request-line</EM>
  %% <EM>HTTP-status</EM> <EM>CGI-script-filename</EM>
</PRE>

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

<PRE>
  %%error
  <EM>error-message</EM>
</PRE>

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:

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

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

<HR>

<H2>Directives</H2>

<H3><A NAME="scriptlog">ScriptLog</A></H3>

<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> ScriptLog <EM>filename</EM><BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A> none<BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> server config<BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> mod_cgi
<P>

The <TT>ScriptLog</TT> 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.

<P>This log will be opened as the user the child processes run as,
ie. the user specified in the main <A HREF="core.html#User">User</A>
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 <STRONG>NOT</STRONG>
change the directory permissions to make it writable by the user
the child processes run as.</P>

<P>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.</P>

<H3><A NAME="scriptloglength">ScriptLogLength</A></H3>

<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> ScriptLogLength <EM>size</EM><BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A> 10385760<BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> server config<BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> mod_cgi
<P>

<TT>ScriptLogLength</TT> 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.

<H3><A NAME="scriptlogbuffer">ScriptLogBuffer</A></H3>

<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> ScriptLogBuffer <EM>size</EM><BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A> 1024<BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> server config<BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> mod_cgi
<P>

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.

<HR>

<H3 ALIGN="CENTER">
 Apache HTTP Server Version 1.3
</H3>

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