MaxClients in Apache with Preforking MPM

The advice for figuring out what your MaxClients setting should be in Apache with the Preforking MPM is pretty straight forward. First figure out the average amount of RAM each Apache process uses. Then divide the amount of RAM your system has, minus a little for other processes, by the average amount of RAM the average Apache process uses. In CentOS the following command should give you that number.

ps -ylC httpd |awk "{ s += \$8 } END { m = `cat /proc/meminfo|grep MemTotal|awk '{print $2}'`; printf \"MaxClients: %i\\n\", (m-(m*.15))/(s/NR) }"