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0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<title>mpm_common - Apache HTTP Server</title>
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0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="/faq/">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<p class="apache">Apache HTTP Server Version 2.3</p>
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ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<div id="preamble"><h1>Apache MPM Common Directives</h1>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<div class="toplang">
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<p><span>Available Languages: </span><a href="/de/mod/mpm_common.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
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ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding</div>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>A collection of directives that are implemented by
0f081398cf0eef8cc7c66a535d450110a92dc8aefieldingmore than one multi-processing module (MPM)</td></tr>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr></table>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding</div>
64185f9824e42f21ca7b9ae6c004484215c031a7rbb<div id="quickview"><h3 class="directives">Directives</h3>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<ul id="toc">
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#coredumpdirectory">CoreDumpDirectory</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#enableexceptionhook">EnableExceptionHook</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#gracefulshutdowntimeout">GracefulShutdownTimeout</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#listen">Listen</a></li>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<li><img alt="" src="/images/down.gif" /> <a href="#listenbacklog">ListenBackLog</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#maxclients">MaxClients</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#maxmemfree">MaxMemFree</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#maxrequestsperchild">MaxRequestsPerChild</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#maxsparethreads">MaxSpareThreads</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#minsparethreads">MinSpareThreads</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#pidfile">PidFile</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#receivebuffersize">ReceiveBufferSize</a></li>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<li><img alt="" src="/images/down.gif" /> <a href="#scoreboardfile">ScoreBoardFile</a></li>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<li><img alt="" src="/images/down.gif" /> <a href="#sendbuffersize">SendBufferSize</a></li>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<li><img alt="" src="/images/down.gif" /> <a href="#serverlimit">ServerLimit</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#startservers">StartServers</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#startthreads">StartThreads</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#threadlimit">ThreadLimit</a></li>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<li><img alt="" src="/images/down.gif" /> <a href="#threadsperchild">ThreadsPerChild</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding<li><img alt="" src="/images/down.gif" /> <a href="#threadstacksize">ThreadStackSize</a></li>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding</ul>
ab2c1c1c83ec91415565da5a71fbc15d9685caa6fielding</div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<div class="directive-section"><h2><a name="CoreDumpDirectory" id="CoreDumpDirectory">CoreDumpDirectory</a> <a name="coredumpdirectory" id="coredumpdirectory">Directive</a></h2>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<table class="directive">
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Directory where Apache attempts to
0f081398cf0eef8cc7c66a535d450110a92dc8aefieldingswitch before dumping core</td></tr>
b6055b7832a0e4d0818416252fff5925aaebae4brbb<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CoreDumpDirectory <var>directory</var></code></td></tr>
2d71630471d1c23f0137309e3c3957c633ecbfd6rbb<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for the default setting</code></td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding</table>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>This controls the directory to which Apache attempts to
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding switch before dumping core. If your operating system is configured to
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding create core files in the working directory of the crashing process,
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <code class="directive">CoreDumpDirectory</code> is necessary to change working
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding directory from the default <code class="directive"><a href="/mod/core.html#serverroot">ServerRoot</a></code>
3d96ee83babeec32482c9082c9426340cee8c44dwrowe directory, which should not be writable by the user the server runs as.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>If you want a core dump for debugging, you can use this directive to
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm place it in a different location. This directive has no effect if your
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding operating system is not configured to write core files to the working directory
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding of the crashing processes.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <div class="note"><h3>Core Dumps on Linux</h3>
4f9a74ad7e44b0464f7cf56525a205d788becacbtrawick <p>If Apache starts as root and switches to another user, the
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding Linux kernel <em>disables</em> core dumps even if the directory is
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding writable for the process. Apache (2.0.46 and later) reenables core dumps
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding on Linux 2.4 and beyond, but only if you explicitly configure a <code class="directive">CoreDumpDirectory</code>.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding </div>
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <div class="note"><h3>Specific signals</h3>
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm <p><code class="directive">CoreDumpDirectory</code> processing only occurs for
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding a select set of fatal signals: SIGFPE, SIGILL, SIGABORT,
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding SIGSEGV, and SIGBUS.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>On some operating systems, SIGQUIT also results in a core dump but
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding does not go through <code class="directive">CoreDumpDirectory</code> or
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <code class="directive">EnableExceptionHook</code> processing, so the core
4f9a74ad7e44b0464f7cf56525a205d788becacbtrawick location is dictated entirely by the operating system.</p>
4f9a74ad7e44b0464f7cf56525a205d788becacbtrawick </div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding</div>
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<div class="directive-section"><h2><a name="EnableExceptionHook" id="EnableExceptionHook">EnableExceptionHook</a> <a name="enableexceptionhook" id="enableexceptionhook">Directive</a></h2>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<table class="directive">
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enables a hook that runs exception handlers
0f081398cf0eef8cc7c66a535d450110a92dc8aefieldingafter a crash</td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>EnableExceptionHook On|Off</code></td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>EnableExceptionHook Off</code></td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.0.49 and later</td></tr>
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm</table>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>For safety reasons this directive is only available if the server was
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding configured with the <code>--enable-exception-hook</code> option. It
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding enables a hook that allows external modules to plug in and do something
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding after a child crashed.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>There are already two modules, <code>mod_whatkilledus</code> and
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <code>mod_backtrace</code> that make use of this hook. Please have a
ca53a74f4012a45cbad48e940eddf27d866981f9dougm look at Jeff Trawick's <a href="http://www.apache.org/~trawick/exception_hook.html">EnableExceptionHook site</a> for more information about these.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
e95f5a6ebefb83d0e8a82cbc4db7d354957a817dben</div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<div class="directive-section"><h2><a name="GracefulShutdownTimeout" id="GracefulShutdownTimeout">GracefulShutdownTimeout</a> <a name="gracefulshutdowntimeout" id="gracefulshutdowntimeout">Directive</a></h2>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<table class="directive">
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Specify a timeout after which a gracefully shutdown server
0f081398cf0eef8cc7c66a535d450110a92dc8aefieldingwill exit.</td></tr>
ca53a74f4012a45cbad48e940eddf27d866981f9dougm<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>GracefulShutDownTimeout <var>seconds</var></code></td></tr>
e95f5a6ebefb83d0e8a82cbc4db7d354957a817dben<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>GracefulShutDownTimeout 0</code></td></tr>
e95f5a6ebefb83d0e8a82cbc4db7d354957a817dben<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
e95f5a6ebefb83d0e8a82cbc4db7d354957a817dben<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
e95f5a6ebefb83d0e8a82cbc4db7d354957a817dben<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code>, <code class="module"><a href="/mod/event.html">event</a></code></td></tr>
e95f5a6ebefb83d0e8a82cbc4db7d354957a817dben<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.2 and later</td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding</table>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>The <code class="directive">GracefulShutdownTimeout</code> specifies
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding how many seconds after receiving a "graceful-stop" signal, a
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm server should continue to run, handling the existing connections.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>Setting this value to zero means that the server will wait
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm indefinitely until all remaining requests have been fully served.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding</div>
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<div class="directive-section"><h2><a name="Listen" id="Listen">Listen</a> <a name="listen" id="listen">Directive</a></h2>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<table class="directive">
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>IP addresses and ports that the server
0f081398cf0eef8cc7c66a535d450110a92dc8aefieldinglistens to</td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>Listen [<var>IP-address</var>:]<var>portnumber</var> [<var>protocol</var>]</code></td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code>, <code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code>, <code class="module"><a href="/mod/event.html">event</a></code></td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Required directive since Apache 2.0<br />
0f081398cf0eef8cc7c66a535d450110a92dc8aefieldingThe <var>protocol</var> argument was added in 2.1.5</td></tr>
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm</table>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>The <code class="directive">Listen</code> directive instructs Apache to
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding listen to only specific IP addresses or ports; by default it
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding responds to requests on all IP interfaces. <code class="directive">Listen</code>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding is now a required directive. If it is not in the config file, the
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding server will fail to start. This is a change from previous versions
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding of Apache.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
8f3ec4772d2aeb347cf40e87c77627bb784dd018rbb <p>The <code class="directive">Listen</code> directive tells the server to
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding accept incoming requests on the specified port or address-and-port
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding combination. If only a port number is specified, the server listens to
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding the given port on all interfaces. If an IP address is given as well
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding as a port, the server will listen on the given port and
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding interface.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
85bea52867bd1a8c81080ba415b5cd5b771ce5f7gstein <p>Multiple <code class="directive">Listen</code> directives may be used to
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding specify a number of addresses and ports to listen to. The server will
d9f2c22804bcbc9ad07d4ec18fbb8aa7c042dcd0bjh respond to requests from any of the listed addresses and ports.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>For example, to make the server accept connections on both
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding port 80 and port 8000, use:</p>
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <div class="example"><p><code>
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm Listen 80<br />
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding Listen 8000
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding </code></p></div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>To make the server accept connections on two specified
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding interfaces and port numbers, use </p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <div class="example"><p><code>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding Listen 192.170.2.1:80<br />
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding Listen 192.170.2.5:8000
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding </code></p></div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
10a4cdd68ef1ca0e54af296fe1d08ac00150c90bwrowe <p>IPv6 addresses must be surrounded in square brackets, as in the
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding following example:</p>
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm <div class="example"><p><code>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding Listen [2001:db8::a00:20ff:fea7:ccea]:80
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm </code></p></div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>The optional <var>protocol</var> argument is not required for most
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding configurations. If not specified, <code>https</code> is the default for
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding port 443 and <code>http</code> the default for all other ports. The
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding protocol is used to determine which module should handle a request, and
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding to apply protocol specific optimizations with the
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <code class="directive"><a href="/mod/core.html#acceptfilter">AcceptFilter</a></code> directive.</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <p>You only need to set the protocol if you are running on non-standard
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding ports. For example, running an <code>https</code> site on port 8443:</p>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <div class="example"><p><code>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding Listen 192.170.2.1:8443 https
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding </code></p></div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding <div class="note"><h3>Error condition</h3>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding Multiple <code class="directive">Listen</code> directives for the same ip
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding address and port will result in an <code>Address already in use</code>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding error message.
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding </div>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<h3>See also</h3>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<ul>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<li><a href="/dns-caveats.html">DNS Issues</a></li>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<li><a href="/bind.html">Setting which addresses and ports Apache
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding uses</a></li>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<li><a href="http://wiki.apache.org/httpd/CouldNotBindToAddress">Further
0f081398cf0eef8cc7c66a535d450110a92dc8aefieldingdiscussion of the <code>Address already in use</code> error message,
0f081398cf0eef8cc7c66a535d450110a92dc8aefieldingincluding other causes.</a></li>
73e8b26287de5c06fa470d36162e103dbac9c7e5wrowe</ul>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding</div>
e95f5a6ebefb83d0e8a82cbc4db7d354957a817dben<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
e95f5a6ebefb83d0e8a82cbc4db7d354957a817dben<div class="directive-section"><h2><a name="ListenBackLog" id="ListenBackLog">ListenBackLog</a> <a name="listenbacklog" id="listenbacklog">Directive</a></h2>
e95f5a6ebefb83d0e8a82cbc4db7d354957a817dben<table class="directive">
e95f5a6ebefb83d0e8a82cbc4db7d354957a817dben<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum length of the queue of pending connections</td></tr>
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ListenBacklog <var>backlog</var></code></td></tr>
3d96ee83babeec32482c9082c9426340cee8c44dwrowe<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ListenBacklog 511</code></td></tr>
fd0edaa8e3d4dd67d0604ccef2e96b071db96643fielding<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
fd0edaa8e3d4dd67d0604ccef2e96b071db96643fielding<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
fd0edaa8e3d4dd67d0604ccef2e96b071db96643fielding<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code>, <code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
fd0edaa8e3d4dd67d0604ccef2e96b071db96643fielding</table>
fd0edaa8e3d4dd67d0604ccef2e96b071db96643fielding <p>The maximum length of the queue of pending connections.
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm Generally no tuning is needed or desired, however on some
e95f5a6ebefb83d0e8a82cbc4db7d354957a817dben systems it is desirable to increase this when under a TCP SYN
0f081398cf0eef8cc7c66a535d450110a92dc8aefielding flood attack. See the backlog parameter to the
<code>listen(2)</code> system call.</p>
<p>This will often be limited to a smaller number by the
operating system. This varies from OS to OS. Also note that
many OSes do not use exactly what is specified as the backlog,
but use a number based on (but normally larger than) what is
set.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="MaxClients" id="MaxClients">MaxClients</a> <a name="maxclients" id="maxclients">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of connections that will be processed
simultaneously</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxClients <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
</table>
<p>The <code class="directive">MaxClients</code> directive sets the limit
on the number of simultaneous requests that will be served. Any
connection attempts over the <code class="directive">MaxClients</code>
limit will normally be queued, up to a number based on the
<code class="directive"><a href="#listenbacklog">ListenBacklog</a></code>
directive. Once a child process is freed at the end of a different
request, the connection will then be serviced.</p>
<p>For non-threaded servers (<em>i.e.</em>, <code class="module"><a href="/mod/prefork.html">prefork</a></code>),
<code class="directive">MaxClients</code> translates into the maximum
number of child processes that will be launched to serve requests.
The default value is <code>256</code>; to increase it, you must also raise
<code class="directive"><a href="#serverlimit">ServerLimit</a></code>.</p>
<p>For threaded and hybrid servers (<em>e.g.</em> <code class="module"><a href="/mod/event.html">event</a></code>
or <code class="module"><a href="/mod/worker.html">worker</a></code>) <code class="directive">MaxClients</code> restricts
the total number of threads that will be available to serve clients.
For hybrid MPMs the default value is <code>16</code> (<code class="directive"><a href="#serverlimit">ServerLimit</a></code>) multiplied by the value of
<code>25</code> (<code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code>). Therefore, to increase <code class="directive">MaxClients</code> to a value that requires more than 16 processes,
you must also raise <code class="directive"><a href="#serverlimit">ServerLimit</a></code>.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="MaxMemFree" id="MaxMemFree">MaxMemFree</a> <a name="maxmemfree" id="maxmemfree">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum amount of memory that the main allocator is allowed
to hold without calling <code>free()</code></td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxMemFree <var>KBytes</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxMemFree 0</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code>, <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code></td></tr>
</table>
<p>The <code class="directive">MaxMemFree</code> directive sets the
maximum number of free Kbytes that the main allocator is allowed
to hold without calling <code>free()</code>. When not set, or when set
to zero, the threshold will be set to unlimited.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="MaxRequestsPerChild" id="MaxRequestsPerChild">MaxRequestsPerChild</a> <a name="maxrequestsperchild" id="maxrequestsperchild">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Limit on the number of requests that an individual child server
will handle during its life</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxRequestsPerChild <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxRequestsPerChild 10000</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code>, <code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
</table>
<p>The <code class="directive">MaxRequestsPerChild</code> directive sets
the limit on the number of requests that an individual child
server process will handle. After
<code class="directive">MaxRequestsPerChild</code> requests, the child
process will die. If <code class="directive">MaxRequestsPerChild</code> is
<code>0</code>, then the process will never expire.</p>
<div class="note"><h3>Different default values</h3>
<p>The default value for <code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code> and
<code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code> is <code>0</code>.</p>
</div>
<p>Setting <code class="directive">MaxRequestsPerChild</code> to a
non-zero value limits the amount of memory that process can consume
by (accidental) memory leakage.</p>
<div class="note"><h3>Note</h3>
<p>For <code class="directive"><a href="/mod/core.html#keepalive">KeepAlive</a></code> requests, only
the first request is counted towards this limit. In effect, it
changes the behavior to limit the number of <em>connections</em> per
child.</p>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="MaxSpareThreads" id="MaxSpareThreads">MaxSpareThreads</a> <a name="maxsparethreads" id="maxsparethreads">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle threads</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareThreads <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
</table>
<p>Maximum number of idle threads. Different MPMs deal with this
directive differently.</p>
<p>For <code class="module"><a href="/mod/worker.html">worker</a></code>, the default is
<code>MaxSpareThreads 250</code>. This MPM deals with idle threads
on a server-wide basis. If there are too many idle threads in the
server then child processes are killed until the number of idle
threads is less than this number.</p>
<p>For <code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code> the default is
<code>MaxSpareThreads 100</code>. Since this MPM runs a
single-process, the spare thread count is also server-wide.</p>
<p><code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code> works
similar to <code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code>. For
<code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code> the default value is <code>10</code>.</p>
<div class="note"><h3>Restrictions</h3>
<p>The range of the <code class="directive">MaxSpareThreads</code> value
is restricted. Apache will correct the given value automatically
according to the following rules:</p>
<ul>
<li><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code> wants the value to be greater than
<code class="directive"><a href="#minsparethreads">MinSpareThreads</a></code>.</li>
<li>For <code class="module"><a href="/mod/worker.html">worker</a></code>, the value must be greater or equal
to the sum of <code class="directive"><a href="#minsparethreads">MinSpareThreads</a></code>
and <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code>.</li>
</ul>
</div>
<h3>See also</h3>
<ul>
<li><code class="directive"><a href="#minsparethreads">MinSpareThreads</a></code></li>
<li><code class="directive"><a href="#startservers">StartServers</a></code></li>
<li><code class="directive"><a href="/mod/prefork.html#maxspareservers">MaxSpareServers</a></code></li>
</ul>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="MinSpareThreads" id="MinSpareThreads">MinSpareThreads</a> <a name="minsparethreads" id="minsparethreads">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle threads available to handle request
spikes</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareThreads <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
</table>
<p>Minimum number of idle threads to handle request spikes.
Different MPMs deal with this directive
differently.</p>
<p><code class="module"><a href="/mod/worker.html">worker</a></code> uses a default of <code>MinSpareThreads
75</code> and deals with idle threads on a server-wide basis. If
there aren't enough idle threads in the server then child
processes are created until the number of idle threads is greater
than <var>number</var>.</p>
<p><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code> uses a default of
<code>MinSpareThreads 10</code> and, since it is a single-process
MPM, tracks this on a server-wide bases.</p>
<p><code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code> works
similar to <code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code>. For
<code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code> the default value is <code>5</code>.</p>
<h3>See also</h3>
<ul>
<li><code class="directive"><a href="#maxsparethreads">MaxSpareThreads</a></code></li>
<li><code class="directive"><a href="#startservers">StartServers</a></code></li>
<li><code class="directive"><a href="/mod/prefork.html#minspareservers">MinSpareServers</a></code></li>
</ul>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="PidFile" id="PidFile">PidFile</a> <a name="pidfile" id="pidfile">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>File where the server records the process ID
of the daemon</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>PidFile <var>filename</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>PidFile logs/httpd.pid</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code>, <code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
</table>
<p>The <code class="directive">PidFile</code> directive sets the file to
which the server records the process id of the daemon. If the
filename is not absolute then it is assumed to be relative to the
<code class="directive"><a href="/mod/core.html#serverroot">ServerRoot</a></code>.</p>
<div class="example"><h3>Example</h3><p><code>
PidFile /var/run/apache.pid
</code></p></div>
<p>It is often useful to be able to send the server a signal,
so that it closes and then re-opens its <code class="directive"><a href="/mod/core.html#errorlog">ErrorLog</a></code> and <code class="directive"><a href="/mod/mod_log_config.html#transferlog">TransferLog</a></code>, and
re-reads its configuration files. This is done by sending a
SIGHUP (kill -1) signal to the process id listed in the
<code class="directive">PidFile</code>.</p>
<p>The <code class="directive">PidFile</code> is subject to the same
warnings about log file placement and <a href="/misc/security_tips.html#serverroot">security</a>.</p>
<div class="note"><h3>Note</h3>
<p>As of Apache 2, we recommended that you only use the <code class="program"><a href="/programs/apachectl.html">apachectl</a></code> script, or the init script that your OS provides,
for (re-)starting or stopping the server.</p>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="ReceiveBufferSize" id="ReceiveBufferSize">ReceiveBufferSize</a> <a name="receivebuffersize" id="receivebuffersize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>TCP receive buffer size</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ReceiveBufferSize <var>bytes</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ReceiveBufferSize 0</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code>, <code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
</table>
<p>The server will set the TCP receive buffer size to the number of
bytes specified.</p>
<p>If set to the value of <code>0</code>, the server will use the
OS default.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="ScoreBoardFile" id="ScoreBoardFile">ScoreBoardFile</a> <a name="scoreboardfile" id="scoreboardfile">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Location of the file used to store coordination data for
the child processes</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ScoreBoardFile <var>file-path</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ScoreBoardFile logs/apache_status</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
</table>
<p>Apache uses a scoreboard to communicate between its parent
and child processes. Some architectures require a file to facilitate
this communication. If the file is left unspecified, Apache first
attempts to create the scoreboard entirely in memory (using anonymous
shared memory) and, failing that, will attempt to create the file on
disk (using file-based shared memory). Specifying this directive causes
Apache to always create the file on the disk.</p>
<div class="example"><h3>Example</h3><p><code>
ScoreBoardFile /var/run/apache_status
</code></p></div>
<p>File-based shared memory is useful for third-party applications
that require direct access to the scoreboard.</p>
<p>If you use a <code class="directive">ScoreBoardFile</code> then
you may see improved speed by placing it on a RAM disk. But be
careful that you heed the same warnings about log file placement
and <a href="/misc/security_tips.html">security</a>.</p>
<h3>See also</h3>
<ul>
<li><a href="/stopping.html">Stopping and Restarting
Apache</a></li>
</ul>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="SendBufferSize" id="SendBufferSize">SendBufferSize</a> <a name="sendbuffersize" id="sendbuffersize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>TCP buffer size</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>SendBufferSize <var>bytes</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>SendBufferSize 0</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code>, <code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
</table>
<p>The server will set the TCP send buffer size to the number of bytes
specified. Very useful to increase past standard OS defaults on
high speed high latency (<em>i.e.</em>, 100ms or so, such as
transcontinental fast pipes).</p>
<p>If set to the value of <code>0</code>, the server will use the
OS default.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="ServerLimit" id="ServerLimit">ServerLimit</a> <a name="serverlimit" id="serverlimit">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Upper limit on configurable number of processes</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ServerLimit <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
</table>
<p>For the <code class="module"><a href="/mod/prefork.html">prefork</a></code> MPM, this directive sets the
maximum configured value for <code class="directive"><a href="#maxclients">MaxClients</a></code> for the lifetime of the
Apache process. For the <code class="module"><a href="/mod/worker.html">worker</a></code> MPM, this directive
in combination with <code class="directive"><a href="#threadlimit">ThreadLimit</a></code> sets
the maximum configured value for <code class="directive"><a href="#maxclients">MaxClients</a></code> for the lifetime of the
Apache process. Any attempts to change this directive during a
restart will be ignored, but <code class="directive"><a href="#maxclients">MaxClients</a></code> can be modified during
a restart.</p>
<p>Special care must be taken when using this directive. If
<code class="directive">ServerLimit</code> is set to a value much higher
than necessary, extra, unused shared memory will be allocated. If
both <code class="directive">ServerLimit</code> and <code class="directive"><a href="#maxclients">MaxClients</a></code> are set to values
higher than the system can handle, Apache may not start or the
system may become unstable.</p>
<p>With the <code class="module"><a href="/mod/prefork.html">prefork</a></code> MPM, use this directive only
if you need to set <code class="directive"><a href="#maxclients">MaxClients</a></code> higher than 256 (default).
Do not set the value of this directive any higher than what you
might want to set <code class="directive"><a href="#maxclients">MaxClients</a></code> to.</p>
<p>With <code class="module"><a href="/mod/worker.html">worker</a></code>, use this directive only
if your <code class="directive"><a href="#maxclients">MaxClients</a></code> and
<code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code>
settings require more than 16 server processes (default). Do not set
the value of this directive any higher than the number of server
processes required by what you may want for <code class="directive"><a href="#maxclients ">MaxClients </a></code> and <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code>.</p>
<div class="note"><h3>Note</h3>
<p>There is a hard limit of <code>ServerLimit 20000</code> compiled
into the server (for the <code class="module"><a href="/mod/prefork.html">prefork</a></code> MPM 200000). This is
intended to avoid nasty effects caused by typos.</p>
</div>
<h3>See also</h3>
<ul>
<li><a href="/stopping.html">Stopping and Restarting Apache</a></li>
</ul>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="StartServers" id="StartServers">StartServers</a> <a name="startservers" id="startservers">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Number of child server processes created at startup</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>StartServers <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code>, <code class="module"><a href="/mod/prefork.html">prefork</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
</table>
<p>The <code class="directive">StartServers</code> directive sets the
number of child server processes created on startup. As the number
of processes is dynamically controlled depending on the load,
there is usually little reason to adjust this parameter.</p>
<p>The default value differs from MPM to MPM. <code class="module"><a href="/mod/worker.html">worker</a></code>
defaults to <code>StartServers 3</code>; <code class="module"><a href="/mod/prefork.html">prefork</a></code>
defaults to <code>5</code>; <code class="module"><a href="/mod/mpmt_os2.html">mpmt_os2</a></code> defaults to
<code>2</code>.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="StartThreads" id="StartThreads">StartThreads</a> <a name="startthreads" id="startthreads">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Number of threads created on startup</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>StartThreads <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code></td></tr>
</table>
<p>Number of threads created on startup. As the
number of threads is dynamically controlled depending on the
load, there is usually little reason to adjust this
parameter.</p>
<p>For <code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code> the default is
<code>StartThreads 50</code> and, since there is only a single
process, this is the total number of threads created at startup to
serve requests.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="ThreadLimit" id="ThreadLimit">ThreadLimit</a> <a name="threadlimit" id="threadlimit">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Sets the upper limit on the configurable number of threads
per child process</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ThreadLimit <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available for <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code> in Apache 2.0.41
and later</td></tr>
</table>
<p>This directive sets the maximum configured value for <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code> for the lifetime
of the Apache process. Any attempts to change this directive
during a restart will be ignored, but <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code> can be modified
during a restart up to the value of this directive.</p>
<p>Special care must be taken when using this directive. If
<code class="directive">ThreadLimit</code> is set to a value much higher
than <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code>,
extra unused shared memory will be allocated. If both
<code class="directive">ThreadLimit</code> and <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code> are set to values
higher than the system can handle, Apache may not start or the
system may become unstable. Do not set the value of this directive
any higher than your greatest predicted setting of <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code> for the
current run of Apache.</p>
<p>The default value for <code class="directive">ThreadLimit</code> is
<code>1920</code> when used with <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code> and
<code>64</code> when used with the others.</p>
<div class="note"><h3>Note</h3>
<p>There is a hard limit of <code>ThreadLimit 20000</code> (or
<code>ThreadLimit 15000</code> with <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>)
compiled into the server. This is intended to avoid nasty effects
caused by typos.</p>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="ThreadsPerChild" id="ThreadsPerChild">ThreadsPerChild</a> <a name="threadsperchild" id="threadsperchild">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Number of threads created by each child process</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ThreadsPerChild <var>number</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
</table>
<p>This directive sets the number of threads created by each
child process. The child creates these threads at startup and
never creates more. If using an MPM like <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>,
where there is only one child process, this number should be high
enough to handle the entire load of the server. If using an MPM
like <code class="module"><a href="/mod/worker.html">worker</a></code>, where there are multiple child processes,
the <em>total</em> number of threads should be high enough to handle
the common load on the server.</p>
<p>The default value for <code class="directive">ThreadsPerChild</code> is
<code>64</code> when used with <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code> and
<code>25</code> when used with the others.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="ThreadStackSize" id="ThreadStackSize">ThreadStackSize</a> <a name="threadstacksize" id="threadstacksize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The size in bytes of the stack used by threads handling
client connections</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ThreadStackSize <var>size</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>65536 on NetWare; varies on other operating systems</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="/mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="/mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="/mod/worker.html">worker</a></code></td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.1 and later</td></tr>
</table>
<p>The <code class="directive">ThreadStackSize</code> directive sets the
size of the stack (for autodata) of threads which handle client
connections and call modules to help process those connections.
In most cases the operating system default for stack size is
reasonable, but there are some conditions where it may need to be
adjusted:</p>
<ul>
<li>On platforms with a relatively small default thread stack size
(e.g., HP-UX), Apache may crash when using some third-party modules
which use a relatively large amount of autodata storage. Those
same modules may have worked fine on other platforms where the
default thread stack size is larger. This type of crash is
resolved by setting <code class="directive">ThreadStackSize</code> to a
value higher than the operating system default. This type of
adjustment is necessary only if the provider of the third-party
module specifies that it is required, or if diagnosis of an Apache
crash indicates that the thread stack size was too small.</li>
<li>On platforms where the default thread stack size is
significantly larger than necessary for the web server
configuration, a higher number of threads per child process
will be achievable if <code class="directive">ThreadStackSize</code> is
set to a value lower than the operating system default. This type
of adjustment should only be made in a test environment which allows
the full set of web server processing can be exercised, as there
may be infrequent requests which require more stack to process.
A change in the web server configuration can invalidate the
current <code class="directive">ThreadStackSize</code> setting.</li>
</ul>
</div>
</div>
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