Apache: The Definitive Guide, Second Edition

3.12. Restarts

A webmaster will sometimes want to kill Apache and restart it with a new Config file, often to add or remove a virtual host. This can be done the brutal way, by stopping httpd and restarting it. This method causes any transactions in progress to fail in what may be an annoying and disconcerting way for the clients. A recent innovation in Apache was a scheme to allow restarts of the main server without suddenly chopping off any child processes that were running.

   There are three ways to restart Apache under Unix:

•    Kill and reload Apache, which then rereads all its Config files and restarts:

  % kill 
                    PID
  % httpd 
                    [
                    flags
                    ]
                 

•    The same effect is achieved with less typing by using the flag -HUP to kill Apache:

  % kill -HUP 
                    PID
                 

•    A graceful restart is achieved with the flag -USR1. This rereads the Config files but lets the child processes run to completion, finishing any client transactions in progress, before they are replaced with updated children. In most cases, this is the best way to proceed, because it won't interrupt people who are browsing at the time (unless ...