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  10 <title>prefork - Apache HTTP Server Version 2.5</title>
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  20 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
  21 <p class="apache">Apache HTTP Server Version 2.5</p>
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  25 <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>
  26 <div id="page-content">
  27 <div id="preamble"><h1>Apache MPM prefork</h1>
  28 <div class="toplang">
  29 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
  30 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
  31 <a href="../fr/mod/prefork.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
  32 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
  33 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
  34 </div>
  35 <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>
  36 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
  37 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_prefork_module</td></tr>
  38 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>prefork.c</td></tr></table>
  39 <h3>Summary</h3>
  40
  41     <p>This Multi-Processing Module (MPM) implements a non-threaded,
  42     pre-forking web server. Each server process may answer incoming
  43     requests, and a parent process manages the size of the server pool.
  44     It is appropriate for sites that need to avoid
  45     threading for compatibility with non-thread-safe libraries.  It
  46     is also the best MPM for isolating each request, so that a problem
  47     with a single request will not affect any other.</p>
  48
  49     <p>This MPM is very self-regulating, so it is rarely necessary to
  50     adjust its configuration directives.  Most important is that
  51     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> be big enough
  52     to handle as many simultaneous requests as you expect to receive, but
  53     small enough to assure that there is enough physical RAM for all
  54     processes.</p>
  55 </div>
  56 <div id="quickview"><h3>Topics</h3>
  57 <ul id="topics">
  58 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
  59 </ul><h3 class="directives">Directives</h3>
  60 <ul id="toc">
  61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
  62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
  63 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li>
  64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
  65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
  66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
  67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
  68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
  69 <li><img alt="" src="../images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li>
  70 <li><img alt="" src="../images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li>
  71 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
  72 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li>
  73 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
  74 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
  75 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
  76 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
  77 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
  78 </ul>
  79 <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__&amp;list_id=144532&amp;product=Apache%20httpd-2&amp;query_format=specific&amp;order=changeddate%20DESC%2Cpriority%2Cbug_severity&amp;component=mpm_prefork">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&amp;component=mpm_prefork">Report a bug</a></li></ul><h3>See also</h3>
  80 <ul class="seealso">
  81 <li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server
  82 uses</a></li>
  83 <li><a href="#comments_section">Comments</a></li></ul></div>
  84 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  85 <div class="section">
  86 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
  87     <p>A single control process is responsible for launching child
  88     processes which listen for connections and serve them when they
  89     arrive. Apache httpd always tries to maintain several <dfn>spare</dfn>
  90     or idle server processes, which stand ready to serve incoming
  91     requests. In this way, clients do not need to wait for a new
  92     child processes to be forked before their requests can be
  93     served.</p>
  94
  95     <p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>,
  96     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>,
  97     <code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and
  98     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> regulate how
  99     the parent process creates children to serve requests. In general,
 100     Apache httpd is very self-regulating, so most sites do not need to
 101     adjust these directives from their default values. Sites which
 102     need to serve more than 256 simultaneous requests may need to
 103     increase <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>,
 104     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
 105     thrashing (swapping memory to disk and back). More information
 106     about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
 107     documentation.</p>
 108
 109     <p>While the parent process is usually started as <code>root</code>
 110     under Unix in order to bind to port 80, the child processes are
 111     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
 112     the privileges of the Apache httpd child processes. The child processes
 113     must be able to read all the content that will be served, but
 114     should have as few privileges beyond that as possible.</p>
 115
 116     <p><code class="directive"><a href="../mod/mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></code>
 117     controls how frequently the server recycles processes by killing
 118     old ones and launching new ones.</p>
 119
 120     <p>This MPM uses the <code>mpm-accept</code> mutex to serialize
 121     access to incoming connections when subject to the thundering herd
 122     problem (generally, when there are multiple listening sockets).
 123     The implementation aspects of this mutex can be configured with the
 124     <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive.  The <a href="../misc/perf-tuning.html">performance hints</a>
 125     documentation has additional information about this mutex.</p>
 126 </div>
 127 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 128 <div class="directive-section"><h2><a name="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a></h2>
 129 <table class="directive">
 130 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle child server processes</td></tr>
 131 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var></code></td></tr>
 132 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</code></td></tr>
 133 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 134 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 135 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 136 </table>
 137     <p>The <code class="directive">MaxSpareServers</code> directive sets the
 138     desired maximum number of <em>idle</em> child server processes. An
 139     idle process is one which is not handling a request. If there are
 140     more than <code class="directive">MaxSpareServers</code> idle, then the
 141     parent process will kill off the excess processes.</p>
 142
 143     <p>Tuning of this parameter should only be necessary on very
 144     busy sites. Setting this parameter to a large number is almost
 145     always a bad idea. If you are trying to set the value equal to or lower than
 146     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache HTTP Server
 147     will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p>
 148
 149 <h3>See also</h3>
 150 <ul>
 151 <li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li>
 152 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 153 <li><code class="directive"><a href="../mod/mpm_common.html#maxsparethreads">MaxSpareThreads</a></code></li>
 154 </ul>
 155 </div>
 156 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 157 <div class="directive-section"><h2><a name="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a></h2>
 158 <table class="directive">
 159 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle child server processes</td></tr>
 160 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr>
 161 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</code></td></tr>
 162 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 163 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 164 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 165 </table>
 166     <p>The <code class="directive">MinSpareServers</code> directive sets the
 167     desired minimum number of <em>idle</em> child server processes. An
 168     idle process is one which is not handling a request. If there are
 169     fewer than <code class="directive">MinSpareServers</code> idle, then the parent
 170     process creates new children: It will spawn one, wait a second, then spawn
 171     two, wait a second, then spawn four, and it will
 172     continue exponentially until it is spawning 32 children per second. It will
 173     stop whenever it satisfies the <code class="directive">MinSpareServers</code>
 174     setting.</p>
 175
 176     <p>Tuning of this parameter should only be necessary on very
 177     busy sites. Setting this parameter to a large number is almost
 178     always a bad idea.</p>
 179
 180 <h3>See also</h3>
 181 <ul>
 182 <li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li>
 183 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 184 <li><code class="directive"><a href="../mod/mpm_common.html#minsparethreads">MinSpareThreads</a></code></li>
 185 </ul>
 186 </div>
 187 </div>
 188 <div class="bottomlang">
 189 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
 190 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
 191 <a href="../fr/mod/prefork.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
 192 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
 193 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
 194 </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>Notice:</strong><br />This is not a Q&amp;A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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