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

    <p>This module provides for forensic logging of the requests made to the
    server</p>

    <p><a href="module-dict.html#Status"
    rel="Help"><strong>Status:</strong></a> Extension<br />
     <a href="module-dict.html#SourceFile"
    rel="Help"><strong>Source File:</strong></a>
    mod_log_forensic.c<br />
     <a href="module-dict.html#ModuleIdentifier"
    rel="Help"><strong>Module Identifier:</strong></a>
    log_forensic_module<br />
     <a href="module-dict.html#Compatibility"
    rel="Help"><strong>Compatibility:</strong></a> Available in
    Version 1.3.30 and later.</p>

    <h2>Summary</h2>

    <p>This module provides for forensic logging of client
    requests. Logging is done before and after processing a request, so the
    forensic log contains two log lines for each request.
    The forensic logger is very strict, which means:</p>

    <ul>
    <li>The format is fixed. You cannot modify the logging format at
    runtime.</li>
    <li>If it cannot write its data, the child process exits immediately
    and may dump core (depends on your
    <code><a href="core.html#coredumpdirectory">CoreDumpDirectory</a></code>
    configuration).</li>
    </ul>

    <p>The <code>check_forensic</code> script, which can be found in the
    distribution's support directory, may be helpful in evaluating the
    forensic log output.</p>

    <p>See also: <a href="../logs.html">Apache Log Files</a>.</p>

    <h2>Directives</h2>

    <ul>
      <li><a href="#forensiclog">ForensicLog</a></li>
    </ul>

    <h2><a id="formats" name="formats">Forensic Log Format</a></h2>

    <p>Each request is logged two times. The first time <em>before</em> it's
    processed further (that is, after receiving the headers). The second log
    entry is written <em>after</em> the request processing at the same time
    where normal logging occurs.</p>

    <p>In order to identify each request, a unique request ID is assigned.
    This forensic ID can be cross logged in the normal transfer log using the
    <code>%{forensic-id}n</code> format string. If you're using
    <code><a href="mod_unique_id.html">mod_unique_id</a></code>, its generated
    ID will be used.</p>

    <p>The first line logs the forensic ID, the request line and all received
    headers, separated by pipe characters (<code>|</code>). A sample line
    looks like the following (all on one line):</p>

    <p><code>
        +yQtJf8CoAB4AAFNXBIEAAAAA|GET /manual/de/images/down.gif
        HTTP/1.1|Host:localhost%3a8080|User-Agent:Mozilla/5.0 (X11;
        U; Linux i686; en-US; rv%3a1.6) Gecko/20040216
        Firefox/0.8|Accept:image/png, <var>etc...</var>
    </code></p>

    <p>The plus character at the beginning indicates that this is first log
    line of this request. The second line just contains a minus character and
    the id again:</p>

    <p><code>
      -yQtJf8CoAB4AAFNXBIEAAAAA
    </code></p>

    <p>The <code>check_forensic</code> script takes as its argument the name
    of the logfile. It looks for those <code>+</code>/<code>-</code> ID pairs
    and complains if a request was not completed.</p>

    <h2>Security Considerations</h2>

    <p>See the <a
    href="../misc/security_tips.html#serverroot">security tips</a>
    document for details on why your security could be compromised
    if the directory where logfiles are stored is writable by
    anyone other than the user that starts the server.</p>

    <hr />

    <h2><a id="forensiclog" name="forensiclog">ForensicLog</a>
    directive</h2>

    <p><a href="directive-dict.html#Syntax"
    rel="Help"><strong>Syntax:</strong></a> ForensicLog
    <var>filename</var>|<var>pipe</var><br />
     <a href="directive-dict.html#Context"
    rel="Help"><strong>Context:</strong></a> server config, virtual
    host<br />
     <a href="directive-dict.html#Module"
    rel="Help"><strong>Module:</strong></a> mod_log_forensic<br />
     <a href="directive-dict.html#Compatibility"
    rel="Help"><strong>Compatibility:</strong></a> Available
    in Version 1.3.30 and above</p>

    <p>The <code>ForensicLog</code> directive is used to
    log requests to the server for forensic analysis. Each log entry
    is assigned unique ID which can be associated with the request
    using the normal <code><a href="mod_log_config.html#customlog">CustomLog</a></code>
    directive. <code>mod_log_forensic</code> creates a token called
    <code>forensic-id</code>, which can be added to the transfer log
    using the <code>%{forensic-id}n</code> format string.</p>

    <p>The argument, which specifies the location to which
    the logs will be written, can take one of the following two
    types of values:</p>

    <dl>
      <dt><var>filename</var></dt>
      <dd>A filename, relative to the <code><a href="core.html#serverroot">ServerRoot</a></code>.</dd>

      <dt><var>pipe</var></dt>
      <dd>The pipe character "<code>|</code>", followed by the path
      to a program to receive the log information on its standard
      input. <strong>Security:</strong> if a program is used, then
      it will be run as the user who started httpd. This will be
      root if the server was started by root; be sure that the
      program is secure.</dd>
    </dl>

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