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8 <title>Stopping and Restarting - Apache HTTP Server</title>
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14 <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>
15 <p class="apache">Apache HTTP Server Version 2.3</p>
16 <img alt="" src="./images/feather.gif" /></div>
17 <div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div>
19 <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 2.3</a></div><div id="page-content"><div id="preamble"><h1>Stopping and Restarting</h1>
21 <p><span>Available Languages: </span><a href="./de/stopping.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
22 <a href="./en/stopping.html" title="English"> en </a> |
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24 <a href="./ja/stopping.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
25 <a href="./ko/stopping.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
28 <p>This document covers stopping and restarting Apache on
29 Unix-like systems. Windows NT, 2000 and XP users should see
30 <a href="platform/windows.html#winsvc">Running Apache as a
31 Service</a> and Windows 9x and ME users should see <a href="platform/windows.html#wincons">Running Apache as a
32 Console Application</a> for information on how to control
33 Apache on those platforms.</p>
35 <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#introduction">Introduction</a></li>
36 <li><img alt="" src="./images/down.gif" /> <a href="#term">Stop Now</a></li>
37 <li><img alt="" src="./images/down.gif" /> <a href="#graceful">Graceful Restart</a></li>
38 <li><img alt="" src="./images/down.gif" /> <a href="#hup">Restart Now</a></li>
39 <li><img alt="" src="./images/down.gif" /> <a href="#gracefulstop">Graceful Stop</a></li>
40 </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>
41 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
43 <h2><a name="introduction" id="introduction">Introduction</a></h2>
45 <p>In order to stop or restart Apache, you must send a signal to
46 the running <code class="program"><a href="./programs/httpd.html">httpd</a></code> processes. There are two ways to
47 send the signals. First, you can use the unix <code>kill</code>
48 command to directly send signals to the processes. You will
49 notice many <code class="program"><a href="./programs/httpd.html">httpd</a></code> executables running on your system,
50 but you should not send signals to any of them except the parent,
51 whose pid is in the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code>. That is to say you
52 shouldn't ever need to send signals to any process except the
53 parent. There are four signals that you can send the parent:
54 <code><a href="#term">TERM</a></code>,
55 <code><a href="#graceful">USR1</a></code>,
56 <code><a href="#hup">HUP</a></code>, and
57 <code><a href="#gracefulstop">WINCH</a></code>, which
58 will be described in a moment.</p>
60 <p>To send a signal to the parent you should issue a command
63 <div class="example"><p><code>kill -TERM `cat /usr/local/apache2/logs/httpd.pid`</code></p></div>
65 <p>The second method of signaling the <code class="program"><a href="./programs/httpd.html">httpd</a></code> processes
66 is to use the <code>-k</code> command line options: <code>stop</code>,
67 <code>restart</code>, <code>graceful</code> and <code>graceful-stop</code>,
68 as described below. These are arguments to the <code class="program"><a href="./programs/httpd.html">httpd</a></code> binary, but we recommend that
69 you send them using the <code class="program"><a href="./programs/apachectl.html">apachectl</a></code> control script, which
70 will pass them through to <code class="program"><a href="./programs/httpd.html">httpd</a></code>.</p>
72 <p>After you have signaled <code class="program"><a href="./programs/httpd.html">httpd</a></code>, you can read about
73 its progress by issuing:</p>
75 <div class="example"><p><code>tail -f /usr/local/apache2/logs/error_log</code></p></div>
77 <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>
78 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
80 <h2><a name="term" id="term">Stop Now</a></h2>
82 <dl><dt>Signal: TERM</dt>
83 <dd><code>apachectl -k stop</code></dd>
86 <p>Sending the <code>TERM</code> or <code>stop</code> signal to
87 the parent causes it to immediately attempt to kill off all of its
88 children. It may take it several seconds to complete killing off
89 its children. Then the parent itself exits. Any requests in
90 progress are terminated, and no further requests are served.</p>
91 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
93 <h2><a name="graceful" id="graceful">Graceful Restart</a></h2>
95 <dl><dt>Signal: USR1</dt>
96 <dd><code>apachectl -k graceful</code></dd>
99 <p>The <code>USR1</code> or <code>graceful</code> signal causes
100 the parent process to <em>advise</em> the children to exit after
101 their current request (or to exit immediately if they're not
102 serving anything). The parent re-reads its configuration files and
103 re-opens its log files. As each child dies off the parent replaces
104 it with a child from the new <em>generation</em> of the
105 configuration, which begins serving new requests immediately.</p>
107 <p>This code is designed to always respect the process control
108 directive of the MPMs, so the number of processes and threads
109 available to serve clients will be maintained at the appropriate
110 values throughout the restart process. Furthermore, it respects
111 <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code> in the
112 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
113 been created, then create enough to pick up the slack. Hence the
114 code tries to maintain both the number of children appropriate for
115 the current load on the server, and respect your wishes with the
116 <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code>
119 <p>Users of <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
120 will notice that the server statistics are <strong>not</strong>
121 set to zero when a <code>USR1</code> is sent. The code was
122 written to both minimize the time in which the server is unable
123 to serve new requests (they will be queued up by the operating
124 system, so they're not lost in any event) and to respect your
125 tuning parameters. In order to do this it has to keep the
126 <em>scoreboard</em> used to keep track of all children across
129 <p>The status module will also use a <code>G</code> to indicate
130 those children which are still serving requests started before
131 the graceful restart was given.</p>
133 <p>At present there is no way for a log rotation script using
134 <code>USR1</code> to know for certain that all children writing
135 the pre-restart log have finished. We suggest that you use a
136 suitable delay after sending the <code>USR1</code> signal
137 before you do anything with the old log. For example if most of
138 your hits take less than 10 minutes to complete for users on
139 low bandwidth links then you could wait 15 minutes before doing
140 anything with the old log.</p>
143 <p>When you issue a restart, a syntax check is first run, to
144 ensure that there are no errors in the configuration files.
145 If your configuration file has errors in it, you will get an
146 error message about that syntax error, and the server will refuse to
147 restart. This avoids the situation where the server halts and then
148 cannot restart, leaving you with a non-functioning server.</p>
150 <p>This still will not
151 guarantee that the server will restart correctly. To check the
152 semantics of the configuration files as well as the syntax, you
153 can try starting <code class="program"><a href="./programs/httpd.html">httpd</a></code> as a non-root user. If there
154 are no errors it will attempt to open its sockets and logs and fail
155 because it's not root (or because the currently running
156 <code class="program"><a href="./programs/httpd.html">httpd</a></code> already has those ports bound). If it fails
157 for any other reason then it's probably a config file error and the error
158 should be fixed before issuing the graceful restart.</p></div>
159 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
160 <div class="section">
161 <h2><a name="hup" id="hup">Restart Now</a></h2>
163 <dl><dt>Signal: HUP</dt>
164 <dd><code>apachectl -k restart</code></dd>
167 <p>Sending the <code>HUP</code> or <code>restart</code> signal to
168 the parent causes it to kill off its children like in
169 <code>TERM</code>, but the parent doesn't exit. It re-reads its
170 configuration files, and re-opens any log files. Then it spawns a
171 new set of children and continues serving hits.</p>
173 <p>Users of <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
174 will notice that the server statistics are set to zero when a
175 <code>HUP</code> is sent.</p>
177 <div class="note">As with a graceful restart, a syntax check is run before the the
178 restart is attempted. If your configuration file has errors in it, the
179 restart will not be attempted, and you will receive notification of the
180 syntax error(s).</div>
181 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
182 <div class="section">
183 <h2><a name="gracefulstop" id="gracefulstop">Graceful Stop</a></h2>
185 <dl><dt>Signal: WINCH</dt>
186 <dd><code>apachectl -k graceful-stop</code></dd>
189 <p>The <code>WINCH</code> or <code>graceful-stop</code> signal causes
190 the parent process to <em>advise</em> the children to exit after
191 their current request (or to exit immediately if they're not
192 serving anything). The parent will then remove its <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> and cease listening on
193 all ports. The parent will continue to run, and monitor children
194 which are handling requests. Once all children have finalised
195 and exited or the timeout specified by the <code class="directive"><a href="./mod/mpm_common.html#gracefulshutdowntimeout">GracefulShutdownTimeout</a></code> has been
196 reached, the parent will also exit. If the timeout is reached,
197 any remaining children will be sent the <code>TERM</code> signal
198 to force them to exit.</p>
200 <p>A <code>TERM</code> signal will immediately terminate the
201 parent process and all children when in the "graceful" state. However
202 as the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> will
203 have been removed, you will not be able to use
204 <code>apachectl</code> or <code>httpd</code> to send this signal,</p>
206 <div class="note"><p>The <code>graceful-stop</code> signal allows you to run multiple
207 identically configured instances of <code class="program"><a href="./programs/httpd.html">httpd</a></code> at the
208 same time. This is a powerful feature when performing graceful
209 upgrades of Apache, however it can also cause deadlocks and race
210 conditions with some configurations.</p>
212 <p>Care has been taken to ensure that on-disk files
213 such as the <code class="directive"><a href="./mod/core.html#lockfile">Lockfile</a></code> and <code class="directive"><a href="./mod/mod_cgid.html#scriptsock">ScriptSock</a></code> files contain the server
214 PID, and should co-exist without problem. However, if a configuration
215 directive, third-party module or persistent CGI utilises any other on-disk
216 lock or state files; care should be taken to ensure that multiple running
217 instances of <code class="program"><a href="./programs/httpd.html">httpd</a></code> do not clobber each others files.</p>
219 <p>You should also be wary of other potential race conditions, such as
220 using <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code> style piped logging. Multiple running
221 instances of <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code> attempting to rotate the same
222 logfiles at the same time may destroy each other's logfiles.</p></div>
224 <div class="bottomlang">
225 <p><span>Available Languages: </span><a href="./de/stopping.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
226 <a href="./en/stopping.html" title="English"> en </a> |
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228 <a href="./ja/stopping.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
229 <a href="./ko/stopping.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
230 </div><div id="footer">
231 <p class="apache">Copyright 2006 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>
232 <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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