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| <title>Stopping and Restarting - Apache HTTP Server</title> |
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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> |
| <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/">Documentation</a> > <a href="./">Version 2.0</a></div><div id="page-content"><div class="retired"><h4>Please note</h4> |
| <p>This document refers to the <strong>2.0</strong> version of Apache httpd, which <strong>is no longer maintained</strong>. Upgrade, and refer to the current version of httpd instead, documented at:</p> |
| <ul><li><a href="http://httpd.apache.org/docs/current/">Current release version of Apache HTTP Server documentation</a></li></ul><p>You may follow <a href="http://httpd.apache.org/docs/current/stopping.html">this link</a> to go to the current version of this document.</p></div><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"> de </a> | |
| <a href="./en/stopping.html" title="English"> en </a> | |
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| <a href="./tr/stopping.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </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> |
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