How to raise ServerLimit and MaxClient
If your server starts getting more and more traffic you’ll need to lift up number of allowed Apache connections. This guide works only on cPanel/WHM powered servers.
The easy way
Log in at WHM and to go to Service Configuration > Apache Configuration > Global Configuration. In there find ServerLimit and MaxClients and set those to some nice value (eg. 1024 or 2048 depends how much memory you have). Save and that should be it.
The geek way
Edit of httpd.conf (usually located at /usr/local/apache/conf folder). It should look something like this (depending on your server specification):
StartServers 5 MinSpareServers 5 MaxSpareServers 10 ServerLimit 1024 MaxClients 1024 MaxRequestsPerChild 10000
Save, Distill settings, restart Apache:
/usr/local/cpanel/bin/apache_conf_distiller --update /scripts/rebuildhttpdconf /etc/init.d/httpd restart
After you do something like this you simply MUST take a look at your Apache error_log file (usually located at /usr/local/apache/logs folder). If you see following line in Apache error_log:
** [warn] WARNING: Attempt to change ServerLimit ignored during restart
You should stop and run the Apache again since ServerLimit can’t be changed by restarting Apache. To do so execute following at SSH:
apachectl stop apachectl start