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You will notice many httpd executables running on your system,
but you should not send signals to any of them except the parent, whose
pid is in the PidFile. 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:
TERM, HUP, and USR1, which will
be described in a moment.
To send a signal to the parent you should issue a command such as:
kill -TERM `cat /usr/local/apache/logs/httpd.pid`
tail -f /usr/local/apache/logs/error_log
As of Apache 1.3 we provide a script src/support/apachectl
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.
Sending the TERM 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.
Sending the HUP signal to the parent causes it to kill off
its children like in TERM 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.
Users of the
status module
will notice that the server statistics are
set to zero when a HUP is sent.
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 below for a method of avoiding this.
Note: prior to release 1.2b9 this code is quite unstable and shouldn't be used at all.
The USR1 signal causes the parent process to advise
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 generation of the
configuration, which begins serving new requests immediately.
This code is designed to always respect the MaxClients, MinSpareServers, and MaxSpareServers settings. Furthermore, it respects StartServers 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.
Users of the
status module
will notice that the server statistics
are not set to zero when a USR1 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 scoreboard used to keep track
of all children across generations.
The status module will also use a G to indicate those
children which are still serving requests started before the graceful
restart was given.
At present there is no way for a log rotation script using
USR1 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 USR1 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.
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