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<title>Apache module mod_log_forensic</title>
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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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