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   8 <title>prefork - Apache HTTP Server</title>
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  19 <p class="apache">Apache HTTP Server Version 2.5</p>
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  23 <a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.5</a> &gt; <a href="./">Modules</a></div>
  24 <div id="page-content">
  25 <div id="preamble"><h1>Apache MPM prefork</h1>
  26 <div class="toplang">
  27 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
  28 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
  29 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
  30 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
  31 </div>
  32 <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>
  33 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
  34 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_prefork_module</td></tr>
  35 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>prefork.c</td></tr></table>
  36 <h3>Summary</h3>
  37
  38     <p>This Multi-Processing Module (MPM) implements a non-threaded,
  39     pre-forking web server. Each server process may answer incoming
  40     requests, and a parent process manages the size of the server pool.
  41     It is appropriate for sites that need to avoid
  42     threading for compatibility with non-thread-safe libraries.  It
  43     is also the best MPM for isolating each request, so that a problem
  44     with a single request will not affect any other.</p>
  45
  46     <p>This MPM is very self-regulating, so it is rarely necessary to
  47     adjust its configuration directives.  Most important is that
  48     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> be big enough
  49     to handle as many simultaneous requests as you expect to receive, but
  50     small enough to assure that there is enough physical RAM for all
  51     processes.</p>
  52 </div>
  53 <div id="quickview"><h3 class="directives">Directives</h3>
  54 <ul id="toc">
  55 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
  56 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
  57 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li>
  58 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
  59 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
  60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
  61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
  62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
  63 <li><img alt="" src="../images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li>
  64 <li><img alt="" src="../images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li>
  65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
  66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li>
  67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
  68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
  69 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
  70 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
  71 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
  72 </ul>
  73 <h3>Topics</h3>
  74 <ul id="topics">
  75 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
  76 </ul><h3>See also</h3>
  77 <ul class="seealso">
  78 <li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server
  79 uses</a></li>
  80 </ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
  81 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  82 <div class="section">
  83 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
  84     <p>A single control process is responsible for launching child
  85     processes which listen for connections and serve them when they
  86     arrive. Apache httpd always tries to maintain several <dfn>spare</dfn>
  87     or idle server processes, which stand ready to serve incoming
  88     requests. In this way, clients do not need to wait for a new
  89     child processes to be forked before their requests can be
  90     served.</p>
  91
  92     <p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>,
  93     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>,
  94     <code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and
  95     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> regulate how
  96     the parent process creates children to serve requests. In general,
  97     Apache httpd is very self-regulating, so most sites do not need to
  98     adjust these directives from their default values. Sites which
  99     need to serve more than 256 simultaneous requests may need to
 100     increase <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>,
 101     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
 102     thrashing (swapping memory to disk and back). More information
 103     about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
 104     documentation.</p>
 105
 106     <p>While the parent process is usually started as <code>root</code>
 107     under Unix in order to bind to port 80, the child processes are
 108     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
 109     the privileges of the Apache httpd child processes. The child processes
 110     must be able to read all the content that will be served, but
 111     should have as few privileges beyond that as possible.</p>
 112
 113     <p><code class="directive"><a href="../mod/mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></code>
 114     controls how frequently the server recycles processes by killing
 115     old ones and launching new ones.</p>
 116
 117     <p>This MPM uses the <code>mpm-accept</code> mutex to serialize
 118     access to incoming connections when subject to the thundering herd
 119     problem (generally, when there are multiple listening sockets).
 120     The implementation aspects of this mutex can be configured with the
 121     <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive.  The <a href="../misc/perf-tuning.html">performance hints</a>
 122     documentation has additional information about this mutex.</p>
 123 </div>
 124 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 125 <div class="directive-section"><h2><a name="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a></h2>
 126 <table class="directive">
 127 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle child server processes</td></tr>
 128 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var></code></td></tr>
 129 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</code></td></tr>
 130 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 131 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 132 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 133 </table>
 134     <p>The <code class="directive">MaxSpareServers</code> directive sets the
 135     desired maximum number of <em>idle</em> child server processes. An
 136     idle process is one which is not handling a request. If there are
 137     more than <code class="directive">MaxSpareServers</code> idle, then the
 138     parent process will kill off the excess processes.</p>
 139
 140     <p>Tuning of this parameter should only be necessary on very
 141     busy sites. Setting this parameter to a large number is almost
 142     always a bad idea. If you are trying to set the value equal to or lower than
 143     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache HTTP Server
 144     will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p>
 145
 146 <h3>See also</h3>
 147 <ul>
 148 <li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li>
 149 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 150 <li><code class="directive"><a href="../mod/mpm_common.html#maxsparethreads">MaxSpareThreads</a></code></li>
 151 </ul>
 152 </div>
 153 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 154 <div class="directive-section"><h2><a name="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a></h2>
 155 <table class="directive">
 156 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle child server processes</td></tr>
 157 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr>
 158 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</code></td></tr>
 159 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 160 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 161 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 162 </table>
 163     <p>The <code class="directive">MinSpareServers</code> directive sets the
 164     desired minimum number of <em>idle</em> child server processes. An
 165     idle process is one which is not handling a request. If there are
 166     fewer than <code class="directive">MinSpareServers</code> idle, then the parent
 167     process creates new children: It will spawn one, wait a second, then spawn
 168     two, wait a second, then spawn four, and it will
 169     continue exponentially until it is spawning 32 children per second. It will
 170     stop whenever it satisfies the <code class="directive">MinSpareServers</code>
 171     setting.</p>
 172
 173     <p>Tuning of this parameter should only be necessary on very
 174     busy sites. Setting this parameter to a large number is almost
 175     always a bad idea.</p>
 176
 177 <h3>See also</h3>
 178 <ul>
 179 <li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li>
 180 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 181 <li><code class="directive"><a href="../mod/mpm_common.html#minsparethreads">MinSpareThreads</a></code></li>
 182 </ul>
 183 </div>
 184 </div>
 185 <div class="bottomlang">
 186 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
 187 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
 188 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
 189 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
 190 </div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>This section is experimental!</strong><br />Comments placed here should not be expected
 191 to last beyond the testing phase of this system, nor do we in any way guarantee that we'll read them.</div><div id="disqus_thread" /><script type="text/javascript"><!--//--><![CDATA[//><!--
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