apache/docs/manual/mod/mod_log_forensic.xml

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<modulesynopsis metafile="mod_log_forensic.xml.meta">

<name>mod_log_forensic</name>
<description>Forensic Logging of the requests made to the server</description>
<status>Extension</status>
<sourcefile>mod_log_forensic.c</sourcefile>
<identifier>log_forensic_module</identifier>
<compatibility><module>mod_unique_id</module> is no longer required since
version 2.1</compatibility>

<summary>
    <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
    <directive module="mpm_common">CoreDumpDirectory</directive>
    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>
</summary>
<seealso><a href="../logs.html">Apache Log Files</a></seealso>
<seealso><module>mod_log_config</module></seealso>

<section id="formats"><title>Forensic Log Format</title>
    <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
    <module>mod_unique_id</module>, 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>

    <example>
        +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>
    </example>

    <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>

    <example>
      -yQtJf8CoAB4AAFNXBIEAAAAA
    </example>

    <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>
</section>

<section id="security"><title>Security Considerations</title>
    <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>
</section>

<directivesynopsis>
<name>ForensicLog</name>
<description>Sets filename of the forensic log</description>
<syntax>ForensicLog <var>filename</var>|<var>pipe</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>The <directive>ForensicLog</directive> 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 <directive module="mod_log_config">CustomLog</directive>
    directive. <module>mod_log_forensic</module> 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 <directive module="core"
      >ServerRoot</directive>.</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 <directive
      module="core">ServerRoot</directive> directive.

      <note type="warning"><title>Security:</title>
      <p>If a program is used, then it will be run as the user who
      started <program>httpd</program>. 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>
      </note>

      <note><title>Note</title>
        <p>When entering a file path on non-Unix platforms, care should be taken
        to make sure that only forward slashes 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>
      </note></dd>
    </dl>
</usage>
</directivesynopsis>

</modulesynopsis>