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    <title>Apache module mod_cgi</title>
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      <h3>Apache HTTP Server Version 1.3</h3>
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    <h1 align="CENTER">Module mod_cgi</h1>

    <p>This module provides for execution of CGI scripts.</p>

    <p><a href="module-dict.html#Status"
    rel="Help"><strong>Status:</strong></a> Base<br />
     <a href="module-dict.html#SourceFile"
    rel="Help"><strong>Source File:</strong></a> mod_cgi.c<br />
     <a href="module-dict.html#ModuleIdentifier"
    rel="Help"><strong>Module Identifier:</strong></a>
    cgi_module</p>

    <h2>Summary</h2>
    <!-- XXX: Should have references to CGI definition/RFC -->
    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. Files that are not in a <a
    href="mod_alias.html#scriptalias">ScriptAlias</a> directory,
    but which are of type <code>application/x-httpd-cgi</code> by
    virtue of an <code>AddType</code> directive, will still not be
    executed by the server unless <code>Options ExecCGI</code> is
    enabled. See the <a
    href="core.html#options"><code>Options</code></a> directive for
    more details. 

    <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.</p>

    <p>For an introduction to using CGI scripts with Apache, see
    our tutorial on <a href="../howto/cgi.html">Dynamic Content
    with CGI</a>.</p>

    <h2>Directives</h2>

    <ul>
      <li><a href="#scriptlog">ScriptLog</a></li>

      <li><a href="#scriptloglength">ScriptLogLength</a></li>

      <li><a href="#scriptlogbuffer">ScriptLogBuffer</a></li>
    </ul>

    <p>See also: <a href="core.html#options">Options</a>, <a
    href="mod_alias.html#scriptalias">ScriptAlias</a>, <a
    href="mod_mime.html#addtype">AddType</a> and <a
    href="mod_mime.html#addhandler">AddHandler</a>.</p>

    <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</dt>

      <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.</dd>

      <dt>REMOTE_IDENT</dt>

      <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.</dd>

      <dt>REMOTE_USER</dt>

      <dd>This will only be set if the CGI script is subject to
      authentication.</dd>
    </dl>

    <h2><a id="cgi_debug" 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. 

    <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 />

    <h3><a id="scriptlog" name="scriptlog">ScriptLog</a>
    directive</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>

    <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>
    <hr />

    <h3><a id="scriptloglength"
    name="scriptloglength">ScriptLogLength</a> directive</h3>
    <a href="directive-dict.html#Syntax"
    rel="Help"><strong>Syntax:</strong></a> ScriptLogLength
    <em>bytes</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.</p>
    <hr />

    <h3><a id="scriptlogbuffer"
    name="scriptlogbuffer">ScriptLogBuffer</a></h3>
    <a href="directive-dict.html#Syntax"
    rel="Help"><strong>Syntax:</strong></a> ScriptLogBuffer
    <em>bytes</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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