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<div id="preamble"><h1>Apache Module mod_log_forensic</h1>
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<p><span>Available Languages: </span><a href="../en/mod/mod_log_forensic.html" title="English">&nbsp;en&nbsp;</a> |
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Forensic Logging of the requests made to the server</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>log_forensic_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_log_forensic.c</td></tr>
<tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.0.50 and later</td></tr></table>
<h3>Summary</h3>

    <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 (depending on your
    <code class="directive"><a href="../mod/mpm_common.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>

    <div class="warning">
      This module was backported from version 2.1 which uses a more powerful
      APR version in order to generate the forensic IDs. If you want to run
      <code class="module"><a href="../mod/mod_log_forensic.html">mod_log_forensic</a></code> in version 2.0, you need to include
      <code class="module"><a href="../mod/mod_unique_id.html">mod_unique_id</a></code> as well.
    </div>
</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#forensiclog">ForensicLog</a></li>
</ul>
<h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#formats">Forensic Log Format</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#security">Security Considerations</a></li>
</ul><h3>See also</h3>
<ul class="seealso">
<li><a href="../logs.html">Apache Log Files</a></li>
<li><code class="module"><a href="../mod/mod_log_config.html">mod_log_config</a></code></li>
</ul></div>
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<div class="section">
<h2><a name="formats" id="formats">Forensic Log Format</a></h2>
    <p>Each request is logged two times. The first time is <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 class="module"><a href="../mod/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>

    <div class="example"><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></div>

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

    <div class="example"><p><code>
      -yQtJf8CoAB4AAFNXBIEAAAAA
    </code></p></div>

    <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>
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<div class="section">
<h2><a name="security" id="security">Security Considerations</a></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>
</div>
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<div class="directive-section"><h2><a name="ForensicLog" id="ForensicLog">ForensicLog</a> <a name="forensiclog" id="forensiclog">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Sets filename of the forensic log</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ForensicLog <var>filename</var>|<var>pipe</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_log_forensic</td></tr>
</table>
    <p>The <code class="directive">ForensicLog</code> directive is used to
    log requests to the server for forensic analysis. Each log entry
    is assigned a unique ID which can be associated with the request
    using the normal <code class="directive"><a href="../mod/mod_log_config.html#customlog">CustomLog</a></code>
    directive. <code class="module"><a href="../mod/mod_log_forensic.html">mod_log_forensic</a></code> takes the unique ID from
    <code class="module"><a href="../mod/mod_unique_id.html">mod_unique_id</a></code>, so you need to load this module as well.
    (This requirement will not be necessary in version 2.1 and later, because
    of a more powerful APR version.) The ID token is attached to the request
    under the name <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 class="directive"><a href="../mod/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. The program name can be specified relative to the <code class="directive"><a href="../mod/core.html#serverroot">ServerRoot</a></code> directive.

      <div class="warning"><h3>Security:</h3>
      <p>If a program is used, then it will be run as the user who
      started <code class="program"><a href="../programs/httpd.html">httpd</a></code>. This will be root if the server was
      started by root; be sure that the program is secure or switches to a
      less privileged user.</p>
      </div>

      <div class="note"><h3>Note</h3>
        <p>When entering a file path on non-Unix platforms, care should be taken
        to make sure that only forward slashed are used even though the platform
        may allow the use of back slashes. In general it is a good idea to always 
        use forward slashes throughout the configuration files.</p>
      </div></dd>
    </dl>

</div>
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