docs/manual/mod/prefork.html.en - httpd - Git at Google

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 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.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>
 <p class="apache">Apache HTTP Server Version 2.2</p>
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 <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 2.2</a> &gt; <a href="./">Modules</a></div>
 <div id="page-content">
 <div class="retired"><h4>Please note</h4>
             <p>This document refers to the <strong>2.2</strong> version of Apache httpd, which is no longer maintained. The active release is documented <a href="http://httpd.apache.org/docs/current">here</a>. If you have not already upgraded, please follow <a href="http://httpd.apache.org/docs/current/upgrading.html">this link</a> for more information.</p>
         <p>You may follow <a href="http://httpd.apache.org/docs/current/mod/prefork.html">this link</a> to go to the current version of this document.</p></div><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">&nbsp;de&nbsp;</a> |
 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="T&#252;rk&#231;e">&nbsp;tr&nbsp;</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&#160;Identifier:</a></th><td>mpm_prefork_module</td></tr>
 <tr><th><a href="module-dict.html#SourceFile">Source&#160;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 that handles requests in a manner similar
     to Apache 1.3.  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#maxclients">MaxClients</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#acceptmutex">AcceptMutex</a></li>
 <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="mpm_common.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#lockfile">LockFile</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</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#maxrequestsperchild">MaxRequestsPerChild</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="mpm_common.html#user">User</a></li>
 </ul>
 <h3>See also</h3>
 <ul class="seealso">
 <li><a href="../bind.html">Setting which addresses and ports Apache
 uses</a></li>
 </ul><ul class="seealso"><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 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#maxclients">MaxClients</a></code> regulate how
     the parent process creates children to serve requests. In general,
     Apache 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#maxclients">MaxClients</a></code>,
     while sites with limited memory may need to decrease <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</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 as a less-privileged user. The <code class="directive"><a href="../mod/mpm_common.html#user">User</a></code> and <code class="directive"><a href="../mod/mpm_common.html#group">Group</a></code> directives are used to set
     the privileges of the Apache 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#maxrequestsperchild">MaxRequestsPerChild</a></code>
     controls how frequently the server recycles processes by killing
     old ones and launching new ones.</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
     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>
 </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 at a maximum rate of 1 per second.</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>
 </ul>
 </div>
 </div>
 <div class="bottomlang">
 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="T&#252;rk&#231;e">&nbsp;tr&nbsp;</a></p>
 </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 Libera.chat, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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	<div id="page-header">
	<p class="menu"><a href="../mod/">Modules</a> \| <a href="../mod/directives.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>
	<p class="apache">Apache HTTP Server Version 2.2</p>
	<img alt="" src="../images/feather.gif" /></div>
	<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
	<div id="path">
	<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.2</a> > <a href="./">Modules</a></div>
	<div id="page-content">
	<div class="retired"><h4>Please note</h4>
	<p>This document refers to the <strong>2.2</strong> version of Apache httpd, which is no longer maintained. The active release is documented <a href="http://httpd.apache.org/docs/current">here</a>. If you have not already upgraded, please follow <a href="http://httpd.apache.org/docs/current/upgrading.html">this link</a> for more information.</p>
	<p>You may follow <a href="http://httpd.apache.org/docs/current/mod/prefork.html">this link</a> to go to the current version of this document.</p></div><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="../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 that handles requests in a manner similar
	to Apache 1.3. 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#maxclients">MaxClients</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#acceptmutex">AcceptMutex</a></li>
	<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="mpm_common.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#lockfile">LockFile</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</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#maxrequestsperchild">MaxRequestsPerChild</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="mpm_common.html#user">User</a></li>
	</ul>
	<h3>See also</h3>
	<ul class="seealso">
	<li><a href="../bind.html">Setting which addresses and ports Apache
	uses</a></li>
	</ul><ul class="seealso"><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 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#maxclients">MaxClients</a></code> regulate how
	the parent process creates children to serve requests. In general,
	Apache 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#maxclients">MaxClients</a></code>,
	while sites with limited memory may need to decrease <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</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 as a less-privileged user. The <code class="directive"><a href="../mod/mpm_common.html#user">User</a></code> and <code class="directive"><a href="../mod/mpm_common.html#group">Group</a></code> directives are used to set
	the privileges of the Apache 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#maxrequestsperchild">MaxRequestsPerChild</a></code>
	controls how frequently the server recycles processes by killing
	old ones and launching new ones.</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
	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>
	</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 at a maximum rate of 1 per second.</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>
	</ul>
	</div>
	</div>
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