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| <title>prefork - Apache HTTP Server Version 2.4</title> |
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| <p class="apache">Apache HTTP Server Version 2.4</p> |
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| <div id="page-content"> |
| <div id="preamble"><h1>Apache MPM prefork</h1> |
| <div class="toplang"> |
| <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> | |
| <a href="../en/mod/prefork.html" title="English"> en </a> | |
| <a href="../fr/mod/prefork.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | |
| <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | |
| <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p> |
| </div> |
| <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Implements a non-threaded, pre-forking web server</td></tr> |
| <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr> |
| <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_prefork_module</td></tr> |
| <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>prefork.c</td></tr></table> |
| <h3>Summary</h3> |
| |
| <p>This Multi-Processing Module (MPM) implements a non-threaded, |
| pre-forking web server. Each server process may answer incoming |
| requests, and a parent process manages the size of the server pool. |
| It is appropriate for sites that need to avoid |
| threading for compatibility with non-thread-safe libraries. It |
| is also the best MPM for isolating each request, so that a problem |
| with a single request will not affect any other.</p> |
| |
| <p>This MPM is very self-regulating, so it is rarely necessary to |
| adjust its configuration directives. Most important is that |
| <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> be big enough |
| to handle as many simultaneous requests as you expect to receive, but |
| small enough to assure that there is enough physical RAM for all |
| processes.</p> |
| </div> |
| <div id="quickview"><h3>Topics</h3> |
| <ul id="topics"> |
| <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li> |
| </ul><h3 class="directives">Directives</h3> |
| <ul id="toc"> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li> |
| <li><img alt="" src="../images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li> |
| <li><img alt="" src="../images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li> |
| </ul> |
| <h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mpm_prefork">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mpm_prefork">Report a bug</a></li></ul><h3>See also</h3> |
| <ul class="seealso"> |
| <li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server |
| uses</a></li> |
| <li><a href="#comments_section">Comments</a></li></ul></div> |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2> |
| <p>A single control process is responsible for launching child |
| processes which listen for connections and serve them when they |
| arrive. Apache httpd always tries to maintain several <dfn>spare</dfn> |
| or idle server processes, which stand ready to serve incoming |
| requests. In this way, clients do not need to wait for a new |
| child processes to be forked before their requests can be |
| served.</p> |
| |
| <p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>, |
| <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, |
| <code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and |
| <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> regulate how |
| the parent process creates children to serve requests. In general, |
| Apache httpd is very self-regulating, so most sites do not need to |
| adjust these directives from their default values. Sites which |
| need to serve more than 256 simultaneous requests may need to |
| increase <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>, |
| while sites with limited memory may need to decrease <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> to keep the server from |
| thrashing (swapping memory to disk and back). More information |
| about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a> |
| documentation.</p> |
| |
| <p>While the parent process is usually started as <code>root</code> |
| under Unix in order to bind to port 80, the child processes are |
| launched by Apache httpd as a less-privileged user. The <code class="directive"><a href="../mod/mod_unixd.html#user">User</a></code> and <code class="directive"><a href="../mod/mod_unixd.html#group">Group</a></code> directives are used to set |
| the privileges of the Apache httpd child processes. The child processes |
| must be able to read all the content that will be served, but |
| should have as few privileges beyond that as possible.</p> |
| |
| <p><code class="directive"><a href="../mod/mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></code> |
| controls how frequently the server recycles processes by killing |
| old ones and launching new ones.</p> |
| |
| <p>This MPM uses the <code>mpm-accept</code> mutex to serialize |
| access to incoming connections when subject to the thundering herd |
| problem (generally, when there are multiple listening sockets). |
| The implementation aspects of this mutex can be configured with the |
| <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive. The <a href="../misc/perf-tuning.html">performance hints</a> |
| documentation has additional information about this mutex.</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="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a></h2> |
| <table class="directive"> |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle child server processes</td></tr> |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var></code></td></tr> |
| <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</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>prefork</td></tr> |
| </table> |
| <p>The <code class="directive">MaxSpareServers</code> directive sets the |
| desired maximum number of <em>idle</em> child server processes. An |
| idle process is one which is not handling a request. If there are |
| more than <code class="directive">MaxSpareServers</code> idle, then the |
| parent process will kill off the excess processes.</p> |
| |
| <p>Tuning of this parameter should only be necessary on very |
| busy sites. Setting this parameter to a large number is almost |
| always a bad idea. If you are trying to set the value equal to or lower than |
| <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache HTTP Server |
| will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p> |
| |
| <h3>See also</h3> |
| <ul> |
| <li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li> |
| <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li> |
| <li><code class="directive"><a href="../mod/mpm_common.html#maxsparethreads">MaxSpareThreads</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="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a></h2> |
| <table class="directive"> |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle child server processes</td></tr> |
| <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr> |
| <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</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>prefork</td></tr> |
| </table> |
| <p>The <code class="directive">MinSpareServers</code> directive sets the |
| desired minimum number of <em>idle</em> child server processes. An |
| idle process is one which is not handling a request. If there are |
| fewer than <code class="directive">MinSpareServers</code> idle, then the parent |
| process creates new children: It will spawn one, wait a second, then spawn |
| two, wait a second, then spawn four, and it will |
| continue exponentially until it is spawning 32 children per second. It will |
| stop whenever it satisfies the <code class="directive">MinSpareServers</code> |
| setting.</p> |
| |
| <p>Tuning of this parameter should only be necessary on very |
| busy sites. Setting this parameter to a large number is almost |
| always a bad idea.</p> |
| |
| <h3>See also</h3> |
| <ul> |
| <li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li> |
| <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li> |
| <li><code class="directive"><a href="../mod/mpm_common.html#minsparethreads">MinSpareThreads</a></code></li> |
| </ul> |
| </div> |
| </div> |
| <div class="bottomlang"> |
| <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> | |
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| <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p> |
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