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From c...@apache.org
Subject cvs commit: httpd-docs-1.3/htdocs/manual stopping.html.en stopping.html
Date Wed, 11 Jul 2001 18:03:51 GMT
coar        01/07/11 11:03:49

  Added:       htdocs/manual stopping.html.en
  Removed:     htdocs/manual stopping.html
  Log:
  	If the .html.html file is going to include it, and we have
  	alternatives, the stopping.html file needs to be replaced with
  	a stopping.html.en file.
  
  Revision  Changes    Path
  1.1                  httpd-docs-1.3/htdocs/manual/stopping.html.en
  
  Index: stopping.html.en
  ===================================================================
  <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
  <HTML>
  <HEAD>
  <TITLE>Stopping and Restarting Apache</TITLE>
  </HEAD>
  
  <!-- Background white, links blue (unvisited), navy (visited), red (active) -->
  <BODY
   BGCOLOR="#FFFFFF"
   TEXT="#000000"
   LINK="#0000FF"
   VLINK="#000080"
   ALINK="#FF0000"
  >
  <!--#include virtual="header.html" -->
  <H1 ALIGN="CENTER">Stopping and Restarting Apache</H1>
  
  <P>This document covers stopping and restarting Apache on Unix
  and Cygwin only. Windows users should see <A HREF="windows.html#signal">Signalling
  Apache when running</A>.</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/core.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>To send a signal to the parent you should issue a command such as:
  <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/core.html#pidfile">PidFile</A> settings.
  
  <P>As of Apache 1.3 we provide a script called <a
  href="programs/apachectl.html">apachectl</a> which can be used to
  start, stop, and restart Apache.  It may need a little customization
  for your system, see the comments at the top of the script.
  
  <H3>TERM Signal: stop now</H3>
  
  <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.
  
  <H3>HUP Signal: restart now</H3>
  
  <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>Users of the
  <A HREF="mod/mod_status.html">status module</A>
  will notice that the server statistics are
  set to zero when a <CODE>HUP</CODE> is sent.
  
  <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.
  
  <H3>USR1 Signal: graceful restart</H3>
  
  <P><STRONG>Note:</STRONG> prior to release 1.2b9 this code is quite unstable
  and shouldn't be used at all.
  
  <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>This code is designed to always respect the
  <A HREF="mod/core.html#maxclients">MaxClients</A>,
  <A HREF="mod/core.html#minspareservers">MinSpareServers</A>,
  and <A HREF="mod/core.html#maxspareservers">MaxSpareServers</A> settings.
  Furthermore, it respects <A HREF="mod/core.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>Users of the
  <A HREF="mod/mod_status.html">status module</A>
  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>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>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><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.
  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.
  
  
  <H3>Appendix: signals and race conditions</H3>
  
  <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>Architectures that use an on disk
  <A HREF="mod/core.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/core.html#scoreboardfile">ScoreBoardFile</a> documentation for a
  architecture uses it.
  
  <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>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.
  
  <!--#include virtual="footer.html" -->
  </BODY>
  </HTML>
  
  
  

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