mirror of
https://github.com/apache/httpd.git
synced 2025-11-06 16:49:32 +03:00
76480f6b72
git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@96736 13f79535-47bb-0310-9956-ffa450edef68
170 lines
12 KiB
XML
170 lines
12 KiB
XML
<?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="<-" 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-project/">Documentation</a> > <a href="./">Version 2.0</a></div><div id="page-content"><div id="preamble"><h1>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
|
|
running</a>.</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></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>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 <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>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>
|
|
|
|
<div class="example"><p><code>kill -TERM `cat /usr/local/apache/logs/httpd.pid`</code></p></div>
|
|
|
|
<p>You can read about its progress by issuing:</p>
|
|
|
|
<div class="example"><p><code>tail -f /usr/local/apache/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>
|
|
|
|
<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>
|
|
</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 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>
|
|
</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 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>
|
|
|
|
<div class="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.</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
|
|
StartServers parameter.</p>
|
|
|
|
<p>Users of the <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 <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.</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 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 <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 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 <code class="directive"><a href="./mod/mpm_common.html#scoreboardfile">ScoreBoardFile</a></code> 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 <code class="directive"><a href="./mod/mpm_common.html#scoreboardfile">ScoreBoardFile</a></code> 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>
|
|
</div></div><div id="footer"><p class="apache">Maintained by the <a href="http://httpd.apache.org/docs-project/">Apache HTTP Server Documentation Project</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> |