Introduction

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`

You can read about its progress by issuing:

tail -f /usr/local/apache/logs/error_log

Modify those examples to match your ServerRoot and PidFile settings.

A shell script called apachectl is provided which automates the processing of signalling Apache. For details about this script, see the documentation on starting Apache.

Stop Now

Signal: TERM: apachectl stop

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.

Graceful Restart

Signal: USR1: apachectl graceful

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.

On certain platforms that do not allow USR1 to be used for a graceful restart, an alternative signal may be used (such as WINCH). The command apachectl graceful will send the right signal for your platform.

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 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. 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 StartServers parameter.

Users of the mod_status 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.

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 -t command line argument (see httpd). 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 cuHTTP/1.1 200 OK Date: Mon, 07 Jul 2025 05:55:12 GMT Server: Apache/2.0.42 (Win32) PHP/5.2.10 Content-Location: stopping.html.en Vary: negotiate,accept-language,accept-charset TCN: choice Accept-Ranges: bytes Content-Length: 12256 Keep-Alive: timeout=15, max=100 Connection: Keep-Alive Content-Type: text/html; charset=ISO-8859-1 Content-Language: en Stopping and Restarting - Apache HTTP Server

Apache > HTTP Server > Documentation > Version 2.0

Stopping and Restarting

This document covers stopping and restarting Apache on Unix-like systems. Windows users should see Signalling Apache when running.

Introduction
Stop Now
Graceful Restart
Restart Now
Appendix: signals and race conditions