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<parentdocument href="./">Virtual Hosts</parentdocument>

<title>File Descriptor Limits</title>

<summary>

<p>When using a large number of Virtual Hosts, Apache may run

out of available file descriptors (sometimes called <cite>file

handles</cite>) if each Virtual Host specifies different log

files. The total number of file descriptors used by Apache is

one for each distinct error log file, one for every other log

file directive, plus 10-20 for internal use. Unix operating

systems limit the number of file descriptors that may be used

by a process; the limit is typically 64, and may usually be

increased up to a large hard-limit.</p>

<p>Although Apache attempts to increase the limit as required,

this may not work if:</p>

<ol>

<li>Your system does not provide the <code>setrlimit()</code>

system call.</li>

<li>The <code>setrlimit(RLIMIT_NOFILE)</code> call does not

function on your system (such as Solaris 2.3)</li>

<li>The number of file descriptors required exceeds the hard

limit.</li>

<li>Your system imposes other limits on file descriptors,

such as a limit on stdio streams only using file descriptors

below 256. (Solaris 2)</li>

</ol>

<p>In the event of problems you can:</p>

<ul>

<li>Reduce the number of log files; don't specify log files

in the <directive type="section" module="core">VirtualHost</directive>

sections, but only log to the main log files. (See <a

href="#splitlogs">Splitting up your log files</a>, below, for more

information on doing this.)</li>

<li>

If you system falls into 1 or 2 (above), then increase the

file descriptor limit before starting Apache, using a

script like

<example>

<code>#!/bin/sh<br />

ulimit -S -n 100<br />

exec httpd</code>

</example>

</li>

</ul>

</summary>

<section id="splitlogs"><title>Splitting up your log files</title>

<p>If you want to log multiple virtual hosts to the same log file, you

may want to split up the log files afterwards in order to run

statistical analysis of the various virtual hosts. This can be

accomplished in the following manner.</p>

<p>First, you will need to add the virtual host information to the log

entries. This can be done using the <directive module="mod_log_config">

LogFormat</directive>

directive, and the <code>%v</code> variable. Add this to the beginning

of your log format string:</p>

<highlight language="config">

LogFormat "%v %h %l %u %t \"%r\" %&gt;s %b" vhost

CustomLog "logs/multiple_vhost_log" vhost

</highlight>

<p>This will create a log file in the common log format, but with the

canonical virtual host (whatever appears in the

<directive module="core">ServerName</directive> directive) prepended to

each line. (See <module>mod_log_config</module> for

more about customizing your log files.)</p>

<p>When you wish to split your log file into its component parts (one

file per virtual host) you can use the program <code><a

href="/programs/other.html">split-logfile</a></code> to accomplish

this. You'll find this program in the <code>support</code> directory

of the Apache distribution.</p>

<p>Run this program with the command:</p>

<example>

split-logfile &lt; /logs/multiple_vhost_log

</example>

<p>This program, when run with the name of your vhost log file, will

generate one file for each virtual host that appears in your log file.

Each file will be called <code>hostname.log</code>.</p>

</section>

</manualpage>