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- <h1 align="center">Stopping and Restarting the Server</h1>
-
+<html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><!--
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+ --><title>Stopping and Restarting - Apache HTTP Server</title><link href="./style/manual.css" type="text/css" rel="stylesheet"></head><body><blockquote><div align="center"><img src="./images/sub.gif" alt="[APACHE DOCUMENTATION]"><h3>Apache HTTP Server Version 2.0</h3></div><h1 align="center">Stopping and Restarting</h1>
<p>This document covers stopping and restarting Apache on
- Unix-like systems. Windows users should see <a
- href="platform/windows.html#signal">Signalling Apache when
+ Unix-like systems. Windows users should see <a href="platform/windows.html#signal">Signalling Apache when
running</a>.</p>
+<ul><li><a href="#introduction">Introduction</a></li><li><a href="#term">Stop Now</a></li><li><a href="#graceful">Graceful Restart</a></li><li><a href="#hup">Restart Now</a></li><li><a href="#race">Appendix: signals and race conditions</a></li></ul><hr><h2><a name="introduction">Introduction</a></h2>
- <p>You will notice many <code>httpd</code> executables running
- on your system, but you should not send signals to any of them
- except the parent, whose pid is in the <a
- href="mod/mpm_common.html#pidfile">PidFile</a>. 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>TERM</code>, <code>HUP</code>, and <code>USR1</code>,
- which will be described in a moment.</p>
+ <p>You will notice many <code>httpd</code> executables running on
+ your system, but you should not send signals to any of them except
+ the parent, whose pid is in the <a href="./mod/mpm_common.html#pidfile" class="directive"><code class="directive">PidFile</code></a>. 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>TERM</code>,
+ <code>HUP</code>, and <code>USR1</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>
- <blockquote>
-<pre>
- kill -TERM `cat /usr/local/apache/logs/httpd.pid`
-</pre>
- </blockquote>
- You can read about its progress by issuing:
-
- <blockquote>
-<pre>
- tail -f /usr/local/apache/logs/error_log
-</pre>
- </blockquote>
- Modify those examples to match your <a
- href="mod/core.html#serverroot">ServerRoot</a> and <a
- href="mod/mpm_common.html#pidfile">PidFile</a> settings.
-
- <p>A shell script called <a
- href="programs/apachectl.html">apachectl</a> is provided which
- automates the processing of signalling Apache. For details
- about this script, see the documentation on <a
- href="invoking.html">starting Apache</a>.</p>
+<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>kill -TERM `cat /usr/local/apache/logs/httpd.pid`</code></td></tr></table></blockquote>
+
+ <p>You can read about its progress by issuing:</p>
+
+<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>tail -f /usr/local/apache/logs/error_log</code></td></tr></table></blockquote>
- <h3>Stop Now</h3>
+ <p>Modify those examples to match your <a href="./mod/core.html#serverroot" class="directive"><code class="directive">ServerRoot</code></a> and <a href="./mod/mpm_common.html#pidfile" class="directive"><code class="directive">PidFile</code></a> settings.</p>
- <p><strong>Signal:</strong> TERM<br />
- <code>apachectl stop</code></p>
+ <p>A shell script called <a href="programs/apachectl.html">apachectl</a> is provided which
+ automates the processing of signalling Apache. For details
+ about this script, see the documentation on <a href="invoking.html">starting Apache</a>.</p>
+<h2><a name="term">Stop Now</a></h2>
+
+<dl><dt>Signal: TERM</dt>
+<dd><code>apachectl stop</code></dd>
+</dl>
<p>Sending the <code>TERM</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>
+<h2><a name="graceful">Graceful Restart</a></h2>
- <h3>Graceful Restart</h3>
-
- <p><strong>Signal:</strong> USR1<br />
- <code>apachectl graceful</code></p>
+<dl><dt>Signal: USR1</dt>
+<dd><code>apachectl graceful</code></dd>
+</dl>
<p>The <code>USR1</code> signal causes the parent process to
<em>advise</em> the children to exit after their current
replaces it with a child from the new <em>generation</em> of
the configuration, which begins serving new requests
immediately.</p>
- <i>On certain platforms that do not allow USR1 to be used for a
+
+ <blockquote><table><tr><td bgcolor="#e0e5f5">On certain platforms that do not allow USR1 to be used for a
graceful restart, an alternative signal may be used (such as
- WINCH). apachectl graceful will send the right signal for your
- platform.</i>
-
- <p>This code is designed to always respect the <a
- href="mod/mpm_common.html#maxclients">MaxClients</a>, <a
- href="mod/prefork.html#minspareservers">MinSpareServers</a>,
- and <a
- href="mod/prefork.html#maxspareservers">MaxSpareServers</a>
- settings. Furthermore, it respects <a
- href="mod/mpm_common.html#startservers">StartServers</a> in the
- following manner: if after one second at least StartServers new
- children have not been created, then create enough to pick up
- the slack. This is to say that the code tries to maintain both
- the number of children appropriate for the current load on the
- server, and respect your wishes with the StartServers
- parameter.</p>
-
- <p>Users of the <a href="mod/mod_status.html">status module</a>
+ WINCH). The command <code>apachectl graceful</code> will send the
+ right signal for your platform.</td></tr></table></blockquote>
+
+ <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
+ <a href="./mod/mpm_common.html#startservers" class="directive"><code class="directive">StartServers</code></a> in the
+ following manner: if after one second at least <a href="./mod/mpm_common.html#startservers" class="directive"><code class="directive">StartServers</code></a> 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
+ StartServers parameter.</p>
+
+ <p>Users of the <code><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
low bandwidth links then you could wait 15 minutes before doing
anything with the old log.</p>
- <p><strong>Note:</strong> If your configuration file has errors
+ <blockquote><table><tr><td bgcolor="#e0e5f5">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.
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 <a
- href="programs/httpd.html">httpd</a>). This still will not
+ command line argument (see <a href="programs/httpd.html">httpd</a>). 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 httpd as a non-root user. If there are no
because it's not root (or because the currently running httpd
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.</p>
+ should be fixed before issuing the graceful restart.</td></tr></table></blockquote>
+<h2><a name="hup">Restart Now</a></h2>
- <h3>Restart Now</h3>
-
- <p><strong>Signal:</strong> HUP<br />
- <code>apachectl restart</code></p>
+<dl><dt>Signal: HUP</dt>
+<dd><code>apachectl restart</code></dd>
+</dl>
<p>Sending the <code>HUP</code> signal to the parent causes it
to kill off its children like in <code>TERM</code> but the
re-opens any log files. Then it spawns a new set of children
and continues serving hits.</p>
- <p>Users of the <a href="mod/mod_status.html">status module</a>
+ <p>Users of <code><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>
- <p><strong>Note:</strong> 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 below for a method of
- avoiding this.</p>
-
- <h3>Appendix: signals and race conditions</h3>
+<blockquote><table><tr><td bgcolor="#e0e5f5">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.</td></tr></table></blockquote>
+<h2><a name="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 simple
be noted that there still do exist race conditions on certain
architectures.</p>
- <p>Architectures that use an on disk <a
- href="mod/mpm_common.html#scoreboardfile">ScoreBoardFile</a> have the
- potential to corrupt their scoreboards. 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 might 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 <a
- href="mod/mpm_common.html#scoreboardfile">ScoreBoardFile</a>
- documentation for a architecture uses it.</p>
-
- <p><code>NEXT</code> and <code>MACHTEN</code> (68k only) have
- small race conditions which can cause a restart/die signal to
- be lost, but should not cause the server to do anything
- otherwise problematic.
- <!-- they don't have sigaction, or we're not using it -djg -->
- </p>
+ <p>Architectures that use an on disk <a href="./mod/mpm_common.html#scoreboardfile" class="directive"><code class="directive">ScoreBoardFile</code></a> have the potential
+ to corrupt their scoreboards. 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 might 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 <a href="./mod/mpm_common.html#scoreboardfile" class="directive"><code class="directive">ScoreBoardFile</code></a> documentation for a
+ architecture uses it.</p>
<p>All architectures have a small race condition in each child
involving the second and subsequent requests on a persistent
-- 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>
- <!--#include virtual="footer.html" -->
- </body>
-</html>
-
+<hr></blockquote><h3 align="center">Apache HTTP Server Version 2.0</h3><a href="./"><img src="./images/index.gif" alt="Index"></a><a href="./"><img src="./images/home.gif" alt="Home"></a></body></html>
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+<?xml version='1.0' encoding='UTF-8' ?>
+<!DOCTYPE manualpage SYSTEM "./style/manualpage.dtd">
+<?xml-stylesheet type="text/xsl" href="./style/manual.en.xsl"?>
+<manualpage>
+<relativepath href="."/>
+
+ <title>Stopping and Restarting</title>
+
+<summary>
+ <p>This document covers stopping and restarting Apache on
+ Unix-like systems. Windows users should see <a
+ href="platform/windows.html#signal">Signalling Apache when
+ running</a>.</p>
+</summary>
+
+<section id="introduction"><title>Introduction</title>
+
+ <p>You will notice many <code>httpd</code> executables running on
+ your system, but you should not send signals to any of them except
+ the parent, whose pid is in the <directive
+ module="mpm_common">PidFile</directive>. 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>TERM</code>,
+ <code>HUP</code>, and <code>USR1</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>
+
+<example>kill -TERM `cat /usr/local/apache/logs/httpd.pid`</example>
+
+ <p>You can read about its progress by issuing:</p>
+
+<example>tail -f /usr/local/apache/logs/error_log</example>
+
+ <p>Modify those examples to match your <directive
+ module="core">ServerRoot</directive> and <directive
+ module="mpm_common">PidFile</directive> settings.</p>
+
+ <p>A shell script called <a
+ href="programs/apachectl.html">apachectl</a> is provided which
+ automates the processing of signalling Apache. For details
+ about this script, see the documentation on <a
+ href="invoking.html">starting Apache</a>.</p>
+</section>
+
+<section id="term"><title>Stop Now</title>
+
+<dl><dt>Signal: TERM</dt>
+<dd><code>apachectl stop</code></dd>
+</dl>
+
+ <p>Sending the <code>TERM</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>
+</section>
+
+<section id="graceful"><title>Graceful Restart</title>
+
+<dl><dt>Signal: USR1</dt>
+<dd><code>apachectl graceful</code></dd>
+</dl>
+
+ <p>The <code>USR1</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>
+
+ <note>On certain platforms that do not allow USR1 to be used for a
+ graceful restart, an alternative signal may be used (such as
+ WINCH). The command <code>apachectl graceful</code> will send the
+ right signal for your platform.</note>
+
+ <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
+ <directive module="mpm_common">StartServers</directive> in the
+ following manner: if after one second at least <directive
+ module="mpm_common">StartServers</directive> 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
+ StartServers parameter.</p>
+
+ <p>Users of the <module>mod_status</module>
+ 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>
+
+ <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 <a
+ href="programs/httpd.html">httpd</a>). 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 httpd 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 httpd
+ 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.</note>
+</section>
+
+<section id="hup"><title>Restart Now</title>
+
+<dl><dt>Signal: HUP</dt>
+<dd><code>apachectl restart</code></dd>
+</dl>
+
+ <p>Sending the <code>HUP</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 <module>mod_status</module>
+ will notice that the server statistics are set to zero when a
+ <code>HUP</code> is sent.</p>
+
+<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.</note>
+</section>
+
+<section id="race"><title>Appendix: signals and race conditions</title>
+
+ <p>Prior to Apache 1.2b9 there were several <em>race
+ conditions</em> involving the restart and die signals (a simple
+ description of race condition is: a time-sensitive problem, as
+ in if something happens at just the wrong time it won't behave
+ as expected). For those architectures that have the "right"
+ feature set we have eliminated as many as we can. But it should
+ be noted that there still do exist race conditions on certain
+ architectures.</p>
+
+ <p>Architectures that use an on disk <directive
+ module="mpm_common">ScoreBoardFile</directive> have the potential
+ to corrupt their scoreboards. 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 might 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 <directive
+ module="mpm_common">ScoreBoardFile</directive> documentation for a
+ architecture 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>
+</section>
+
+</manualpage>
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