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+<?xml version="1.0" encoding="ISO-8859-1"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
+ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+ This file is generated from xml source: DO NOT EDIT
+ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+ -->
+<title>Stopping and Restarting - Apache HTTP Server</title>
+<link href="./style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
+<link href="./style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
+<link href="./style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" />
+<link href="./images/favicon.ico" rel="shortcut icon" /></head>
+<body id="manual-page"><div id="page-header">
+<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>
+<p class="apache">Apache HTTP Server Version 2.0</p>
+<img alt="" src="./images/feather.gif" /></div>
+<div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="./images/left.gif" /></a></div>
+<div id="path">
+<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 2.0</a></div><div id="page-content"><div id="preamble"><h1>Stopping and Restarting</h1>
+<div class="toplang">
+<p><span>Available Languages: </span><a href="./de/stopping.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
+<a href="./en/stopping.html" title="English">&nbsp;en&nbsp;</a> |
+<a href="./es/stopping.html" hreflang="es" rel="alternate" title="Español">&nbsp;es&nbsp;</a> |
+<a href="./ja/stopping.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
+<a href="./ko/stopping.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
+<a href="./ru/stopping.html" hreflang="ru" rel="alternate" title="Russian">&nbsp;ru&nbsp;</a> |
+<a href="./tr/stopping.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
+</div>
+
+ <p>This document covers stopping and restarting Apache on
+ Unix-like systems. Windows NT, 2000 and XP users should see
+ <a href="platform/windows.html#winsvc">Running Apache as a
+ Service</a> and Windows 9x and ME users should see <a href="platform/windows.html#wincons">Running Apache as a
+ Console Application</a> for information on how to control
+ Apache on those platforms.</p>
+</div>
+<div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#introduction">Introduction</a></li>
+<li><img alt="" src="./images/down.gif" /> <a href="#term">Stop Now</a></li>
+<li><img alt="" src="./images/down.gif" /> <a href="#graceful">Graceful Restart</a></li>
+<li><img alt="" src="./images/down.gif" /> <a href="#hup">Restart Now</a></li>
+<li><img alt="" src="./images/down.gif" /> <a href="#race">Appendix: signals and race conditions</a></li>
+</ul><h3>See also</h3><ul class="seealso"><li><code class="program"><a href="./programs/httpd.html">httpd</a></code></li><li><code class="program"><a href="./programs/apachectl.html">apachectl</a></code></li><li><a href="invoking.html">Starting</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="introduction" id="introduction">Introduction</a></h2>
+
+ <p>In order to stop or restart Apache, you must send a signal to
+ the running <code class="program"><a href="./programs/httpd.html">httpd</a></code> processes. There are two ways to
+ send the signals. First, you can use the unix <code>kill</code>
+ command to directly send signals to the processes. You will
+ notice many <code class="program"><a href="./programs/httpd.html">httpd</a></code> executables running on your system,
+ but you should not send signals to any of them except the parent,
+ whose pid is in the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code>. That is to say you
+ shouldn't ever need to send signals to any process except the
+ parent. There are three signals that you can send the parent:
+ <code><a href="#term">TERM</a></code>,
+ <code><a href="#hup">HUP</a></code>, and
+ <code><a href="#graceful">USR1</a></code>, which
+ will be described in a moment.</p>
+
+ <p>To send a signal to the parent you should issue a command
+ such as:</p>
+
+<div class="example"><p><code>kill -TERM `cat /usr/local/apache2/logs/httpd.pid`</code></p></div>
+
+ <p>The second method of signaling the <code class="program"><a href="./programs/httpd.html">httpd</a></code> processes
+ is to use the <code>-k</code> command line options: <code>stop</code>,
+ <code>restart</code>, and <code>graceful</code>,
+ as described below. These are arguments to the <code class="program"><a href="./programs/httpd.html">httpd</a></code> binary, but we recommend that
+ you send them using the <code class="program"><a href="./programs/apachectl.html">apachectl</a></code> control script, which
+ will pass them through to <code class="program"><a href="./programs/httpd.html">httpd</a></code>.</p>
+
+ <p>After you have signaled <code class="program"><a href="./programs/httpd.html">httpd</a></code>, you can read about
+ its progress by issuing:</p>
+
+<div class="example"><p><code>tail -f /usr/local/apache2/logs/error_log</code></p></div>
+
+ <p>Modify those examples to match your <code class="directive"><a href="./mod/core.html#serverroot">ServerRoot</a></code> and <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> settings.</p>
+</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="term" id="term">Stop Now</a></h2>
+
+<dl><dt>Signal: TERM</dt>
+<dd><code>apachectl -k stop</code></dd>
+</dl>
+
+ <p>Sending the <code>TERM</code> or <code>stop</code> signal to
+ the parent causes it to immediately attempt to kill off all of its
+ children. It may take it several seconds to complete killing off
+ its children. Then the parent itself exits. Any requests in
+ progress are terminated, and no further requests are served.</p>
+</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="graceful" id="graceful">Graceful Restart</a></h2>
+
+<dl><dt>Signal: USR1</dt>
+<dd><code>apachectl -k graceful</code></dd>
+</dl>
+
+ <p>The <code>USR1</code> or <code>graceful</code> signal causes
+ the parent process to <em>advise</em> the children to exit after
+ their current request (or to exit immediately if they're not
+ serving anything). The parent re-reads its configuration files and
+ re-opens its log files. As each child dies off the parent replaces
+ it with a child from the new <em>generation</em> of the
+ configuration, which begins serving new requests immediately.</p>
+
+ <div class="note">On certain platforms that do not allow <code>USR1</code> to
+ be used for a graceful restart, an alternative signal may be used (such
+ as <code>WINCH</code>). The command <code>apachectl graceful</code>
+ will send the right signal for your platform.</div>
+
+ <p>This code is designed to always respect the process control
+ directive of the MPMs, so the number of processes and threads
+ available to serve clients will be maintained at the appropriate
+ values throughout the restart process. Furthermore, it respects
+ <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code> in the
+ following manner: if after one second at least <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code> new children have not
+ been created, then create enough to pick up the slack. Hence the
+ code tries to maintain both the number of children appropriate for
+ the current load on the server, and respect your wishes with the
+ <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code>
+ parameter.</p>
+
+ <p>Users of <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
+ will notice that the server statistics are <strong>not</strong>
+ set to zero when a <code>USR1</code> is sent. The code was
+ written to both minimize the time in which the server is unable
+ to serve new requests (they will be queued up by the operating
+ system, so they're not lost in any event) and to respect your
+ tuning parameters. In order to do this it has to keep the
+ <em>scoreboard</em> used to keep track of all children across
+ generations.</p>
+
+ <p>The status module will also use a <code>G</code> to indicate
+ those children which are still serving requests started before
+ the graceful restart was given.</p>
+
+ <p>At present there is no way for a log rotation script using
+ <code>USR1</code> to know for certain that all children writing
+ the pre-restart log have finished. We suggest that you use a
+ suitable delay after sending the <code>USR1</code> signal
+ before you do anything with the old log. For example if most of
+ your hits take less than 10 minutes to complete for users on
+ low bandwidth links then you could wait 15 minutes before doing
+ anything with the old log.</p>
+
+ <div class="note">If your configuration file has errors
+ in it when you issue a restart then your parent will not
+ restart, it will exit with an error. In the case of graceful
+ restarts it will also leave children running when it exits.
+ (These are the children which are "gracefully exiting" by
+ handling their last request.) This will cause problems if you
+ attempt to restart the server -- it will not be able to bind to
+ its listening ports. Before doing a restart, you can check the
+ syntax of the configuration files with the <code>-t</code>
+ command line argument (see <code class="program"><a href="./programs/httpd.html">httpd</a></code>). This still will not
+ guarantee that the server will restart correctly. To check the
+ semantics of the configuration files as well as the syntax, you
+ can try starting <code class="program"><a href="./programs/httpd.html">httpd</a></code> as a non-root user. If there
+ are no errors it will attempt to open its sockets and logs and fail
+ because it's not root (or because the currently running
+ <code class="program"><a href="./programs/httpd.html">httpd</a></code> already has those ports bound). If it fails
+ for any other reason then it's probably a config file error and the error
+ should be fixed before issuing the graceful restart.</div>
+</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="hup" id="hup">Restart Now</a></h2>
+
+<dl><dt>Signal: HUP</dt>
+<dd><code>apachectl -k restart</code></dd>
+</dl>
+
+ <p>Sending the <code>HUP</code> or <code>restart</code> signal to
+ the parent causes it to kill off its children like in
+ <code>TERM</code>, but the parent doesn't exit. It re-reads its
+ configuration files, and re-opens any log files. Then it spawns a
+ new set of children and continues serving hits.</p>
+
+ <p>Users of <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
+ will notice that the server statistics are set to zero when a
+ <code>HUP</code> is sent.</p>
+
+<div class="note">If your configuration file has errors in it when you issue a
+restart then your parent will not restart, it will exit with an
+error. See above for a method of avoiding this.</div>
+</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="race" id="race">Appendix: signals and race conditions</a></h2>
+
+ <p>Prior to Apache 1.2b9 there were several <em>race
+ conditions</em> involving the restart and die signals (a simply put,
+ a race condition is a time-sensitive problem - if something happens
+ at just the wrong time or things happen in the wrong order,
+ undesired behaviour will result. If the same thing happens at the right
+ time, all will be well). For those architectures that have the "right"
+ feature set we have eliminated as many as we can. But it should
+ be noted that race conditions do still exist on certain
+ architectures.</p>
+
+ <p>Architectures that use an on-disk <code class="directive"><a href="./mod/mpm_common.html#scoreboardfile">ScoreBoardFile</a></code> can potentially have
+ their scoreboards corrupted. This can result in the "bind:
+ Address already in use" (after <code>HUP</code>) or "long lost
+ child came home!" (after <code>USR1</code>). The former is a fatal
+ error, while the latter just causes the server to lose a
+ scoreboard slot. So it may be advisable to use graceful
+ restarts, with an occasional hard restart. These problems are very
+ difficult to work around, but fortunately most architectures do
+ not require a scoreboard file. See the <code class="directive"><a href="./mod/mpm_common.html#scoreboardfile">ScoreBoardFile</a></code> documentation for
+ architecture which uses it.</p>
+
+ <p>All architectures have a small race condition in each child
+ involving the second and subsequent requests on a persistent
+ HTTP connection (KeepAlive). It may exit after reading the
+ request line but before reading any of the request headers.
+ There is a fix that was discovered too late to make 1.2. In
+ theory this isn't an issue because the KeepAlive client has to
+ expect these events because of network latencies and server
+ timeouts. In practice it doesn't seem to affect anything either
+ -- in a test case the server was restarted twenty times per
+ second and clients successfully browsed the site without
+ getting broken images or empty documents. </p>
+</div></div>
+<div class="bottomlang">
+<p><span>Available Languages: </span><a href="./de/stopping.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
+<a href="./en/stopping.html" title="English">&nbsp;en&nbsp;</a> |
+<a href="./es/stopping.html" hreflang="es" rel="alternate" title="Español">&nbsp;es&nbsp;</a> |
+<a href="./ja/stopping.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
+<a href="./ko/stopping.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
+<a href="./ru/stopping.html" hreflang="ru" rel="alternate" title="Russian">&nbsp;ru&nbsp;</a> |
+<a href="./tr/stopping.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
+</div><div id="footer">
+<p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
+<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></div>
+</body></html> \ No newline at end of file