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227 lines
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227 lines
14 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
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This file is generated from xml source: DO NOT EDIT
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<title>Stopping and Restarting - Apache HTTP Server</title>
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<link href="./style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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<link href="./style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
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<link href="./style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" />
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<link href="./images/favicon.ico" rel="shortcut icon" /></head>
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<body id="manual-page"><div id="page-header">
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<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>
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<p class="apache">Apache HTTP Server Version 2.1</p>
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<img alt="" src="./images/feather.gif" /></div>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div>
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<div id="path">
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="./">Version 2.1</a></div><div id="page-content"><div id="preamble"><h1>Stopping and Restarting</h1>
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<div class="toplang">
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<p><span>Available Languages: </span><a href="./de/stopping.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
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<a href="./en/stopping.html" title="English"> en </a> |
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<a href="./ja/stopping.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
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<a href="./ko/stopping.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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</div>
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<p>This document covers stopping and restarting Apache on
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Unix-like systems. Windows NT, 2000 and XP users should see
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<a href="platform/windows.html#winsvc">Running Apache as a
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Service</a> and Windows 9x and ME users should see <a href="platform/windows.html#wincons">Running Apache as a
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Console Application</a> for information on how to control
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Apache on those platforms.</p>
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</div>
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<div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#introduction">Introduction</a></li>
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<li><img alt="" src="./images/down.gif" /> <a href="#term">Stop Now</a></li>
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<li><img alt="" src="./images/down.gif" /> <a href="#graceful">Graceful Restart</a></li>
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<li><img alt="" src="./images/down.gif" /> <a href="#hup">Restart Now</a></li>
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<li><img alt="" src="./images/down.gif" /> <a href="#race">Appendix: signals and race conditions</a></li>
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</ul><h3>See also</h3><ul class="seealso"><li><a href="programs/httpd.html">httpd</a></li><li><a href="programs/apachectl.html">apachectl</a></li></ul></div>
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<div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="introduction" id="introduction">Introduction</a></h2>
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<p>In order to stop or restart Apache, you must send a signal to
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the running <code>httpd</code> processes. There are two ways to
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send the signals. First, you can use the unix <code>kill</code>
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command to directly send signals to the processes. You will
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notice many <code>httpd</code> executables running on your system,
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but you should not send signals to any of them except the parent,
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whose pid is in the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code>. That is to say you
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shouldn't ever need to send signals to any process except the
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parent. There are three signals that you can send the parent:
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<code><a href="#term">TERM</a></code>,
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<code><a href="#hup">HUP</a></code>, and
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<code><a href="#graceful">USR1</a></code>, which
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will be described in a moment.</p>
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<p>To send a signal to the parent you should issue a command
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such as:</p>
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<div class="example"><p><code>kill -TERM `cat /usr/local/apache2/logs/httpd.pid`</code></p></div>
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<p>The second method of signaling the <code>httpd</code> processes
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is to use the <code>-k</code> command line options: <code>stop</code>,
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<code>restart</code>, and <code>graceful</code>,
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as described below. These are arguments to the <a href="programs/httpd.html">httpd</a> binary, but we recommend that
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you send them using the <a href="programs/apachectl.html">apachectl</a> control script, which
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will pass them through to <code>httpd</code>.</p>
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<p>After you have signaled <code>httpd</code>, you can read about
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its progress by issuing:</p>
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<div class="example"><p><code>tail -f /usr/local/apache2/logs/error_log</code></p></div>
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<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>
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</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="term" id="term">Stop Now</a></h2>
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<dl><dt>Signal: TERM</dt>
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<dd><code>apachectl -k stop</code></dd>
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</dl>
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<p>Sending the <code>TERM</code> or <code>stop</code> signal to
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the parent causes it to immediately attempt to kill off all of its
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children. It may take it several seconds to complete killing off
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its children. Then the parent itself exits. Any requests in
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progress are terminated, and no further requests are served.</p>
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</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="graceful" id="graceful">Graceful Restart</a></h2>
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<dl><dt>Signal: USR1</dt>
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<dd><code>apachectl -k graceful</code></dd>
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</dl>
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<p>The <code>USR1</code> or <code>graceful</code> signal causes
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the parent process to <em>advise</em> the children to exit after
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their current request (or to exit immediately if they're not
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serving anything). The parent re-reads its configuration files and
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re-opens its log files. As each child dies off the parent replaces
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it with a child from the new <em>generation</em> of the
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configuration, which begins serving new requests immediately.</p>
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<div class="note">On certain platforms that do not allow <code>USR1</code> to
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be used for a graceful restart, an alternative signal may be used (such
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as <code>WINCH</code>). The command <code>apachectl graceful</code>
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will send the right signal for your platform.</div>
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<p>This code is designed to always respect the process control
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directive of the MPMs, so the number of processes and threads
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available to serve clients will be maintained at the appropriate
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values throughout the restart process. Furthermore, it respects
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<code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code> in the
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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
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been created, then create enough to pick up the slack. Hence the
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code tries to maintain both the number of children appropriate for
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the current load on the server, and respect your wishes with the
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<code class="directive">StartServers</code> parameter.</p>
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<p>Users of the <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
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will notice that the server statistics are <strong>not</strong>
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set to zero when a <code>USR1</code> is sent. The code was
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written to both minimize the time in which the server is unable
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to serve new requests (they will be queued up by the operating
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system, so they're not lost in any event) and to respect your
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tuning parameters. In order to do this it has to keep the
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<em>scoreboard</em> used to keep track of all children across
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generations.</p>
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<p>The status module will also use a <code>G</code> to indicate
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those children which are still serving requests started before
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the graceful restart was given.</p>
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<p>At present there is no way for a log rotation script using
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<code>USR1</code> to know for certain that all children writing
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the pre-restart log have finished. We suggest that you use a
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suitable delay after sending the <code>USR1</code> signal
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before you do anything with the old log. For example if most of
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your hits take less than 10 minutes to complete for users on
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low bandwidth links then you could wait 15 minutes before doing
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anything with the old log.</p>
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<div class="note">If your configuration file has errors
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in it when you issue a restart then your parent will not
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restart, it will exit with an error. In the case of graceful
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restarts it will also leave children running when it exits.
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(These are the children which are "gracefully exiting" by
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handling their last request.) This will cause problems if you
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attempt to restart the server -- it will not be able to bind to
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its listening ports. Before doing a restart, you can check the
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syntax of the configuration files with the <code>-t</code>
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command line argument (see <a href="programs/httpd.html">httpd</a>). This still will not
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guarantee that the server will restart correctly. To check the
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semantics of the configuration files as well as the syntax, you
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can try starting <code>httpd</code> as a non-root user. If there are no
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errors it will attempt to open its sockets and logs and fail
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because it's not root (or because the currently running <code>httpd</code>
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already has those ports bound). If it fails for any other
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reason then it's probably a config file error and the error
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should be fixed before issuing the graceful restart.</div>
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</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="hup" id="hup">Restart Now</a></h2>
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<dl><dt>Signal: HUP</dt>
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<dd><code>apachectl -k restart</code></dd>
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</dl>
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<p>Sending the <code>HUP</code> or <code>restart</code> signal to
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the parent causes it to kill off its children like in
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<code>TERM</code>, but the parent doesn't exit. It re-reads its
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configuration files, and re-opens any log files. Then it spawns a
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new set of children and continues serving hits.</p>
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<p>Users of <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
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will notice that the server statistics are set to zero when a
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<code>HUP</code> is sent.</p>
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<div class="note">If your configuration file has errors in it when you issue a
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restart then your parent will not restart, it will exit with an
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error. See above for a method of avoiding this.</div>
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</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="race" id="race">Appendix: signals and race conditions</a></h2>
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<p>Prior to Apache 1.2b9 there were several <em>race
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conditions</em> involving the restart and die signals (a simple
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description of race condition is: a time-sensitive problem, as
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in if something happens at just the wrong time it won't behave
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as expected). For those architectures that have the "right"
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feature set we have eliminated as many as we can. But it should
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be noted that there still do exist race conditions on certain
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architectures.</p>
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<p>Architectures that use an on disk <code class="directive"><a href="./mod/mpm_common.html#scoreboardfile">ScoreBoardFile</a></code> have the potential
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to corrupt their scoreboards. This can result in the "bind:
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Address already in use" (after <code>HUP</code>) or "long lost
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child came home!" (after <code>USR1</code>). The former is a fatal
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error, while the latter just causes the server to lose a
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scoreboard slot. So it might be advisable to use graceful
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restarts, with an occasional hard restart. These problems are very
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difficult to work around, but fortunately most architectures do
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not require a scoreboard file. See the <code class="directive"><a href="./mod/mpm_common.html#scoreboardfile">ScoreBoardFile</a></code> documentation for a
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architecture uses it.</p>
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<p>All architectures have a small race condition in each child
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involving the second and subsequent requests on a persistent
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HTTP connection (KeepAlive). It may exit after reading the
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request line but before reading any of the request headers.
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There is a fix that was discovered too late to make 1.2. In
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theory this isn't an issue because the KeepAlive client has to
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expect these events because of network latencies and server
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timeouts. In practice it doesn't seem to affect anything either
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-- in a test case the server was restarted twenty times per
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second and clients successfully browsed the site without
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getting broken images or empty documents. </p>
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</div></div>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="./de/stopping.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
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<a href="./en/stopping.html" title="English"> en </a> |
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<a href="./ja/stopping.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
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<a href="./ko/stopping.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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</div><div id="footer">
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<p class="apache">Copyright 1999-2004 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>
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<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>
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