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Apache官方在今天放出产品系列2.2的最新版本2.2.11的源码包 最流行的HTTP服务器软件之一

    <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="gracefulstop" id="gracefulstop">Graceful Stop</a></h2>

<dl><dt>Signal: WINCH</dt>
<dd><code>apachectl -k graceful-stop</code></dd>
</dl>

    <p>The <code>WINCH</code> or <code>graceful-stop</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 will then remove its <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> and cease listening on
    all ports. The parent will continue to run, and monitor children
    which are handling requests. Once all children have finalised
    and exited or the timeout specified by the <code class="directive"><a href="./mod/mpm_common.html#gracefulshutdowntimeout">GracefulShutdownTimeout</a></code> has been
    reached, the parent will also exit.  If the timeout is reached,
    any remaining children will be sent the <code>TERM</code> signal
    to force them to exit.</p>
    
    <p>A <code>TERM</code> signal will immediately terminate the 
    parent process and all children when in the "graceful" state. However
    as the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> will
    have been removed, you will not be able to use 
    <code>apachectl</code> or <code>httpd</code> to send this signal.</p>

    <div class="note"><p>The <code>graceful-stop</code> signal allows you to run multiple
    identically configured instances of <code class="program"><a href="./programs/httpd.html">httpd</a></code> at the 
    same time. This is a powerful feature when performing graceful 
    upgrades of Apache, however it can also cause deadlocks and race 
    conditions with some configurations.</p> 

    <p>Care has been taken to ensure that on-disk files
    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
    PID, and should coexist without problem. However, if a configuration
    directive, third-party module or persistent CGI utilises any other on-disk 
    lock or  state files, care should be taken to ensure that multiple running 
    instances of <code class="program"><a href="./programs/httpd.html">httpd</a></code> do not clobber each others files.</p> 

    <p>You should also be wary of other potential race conditions, such as
    using <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code> style piped logging. Multiple running
    instances of <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code> attempting to rotate the same
    logfiles at the same time may destroy each other's logfiles.</p></div>
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