The mod_ruid2 Apache module changes the permissions of all of the HTTP requests for a domain to the permissions of the owner of that domain. This is just like suexec or the module mod_suphp !
If you have enabled mod_ruid2 in your server and if there are any scripts which require mutual exclusion to take place, there might be some issues being reported by Apache.
You might find something like this in the Apache error logs :
Date [emerg] (13)Permission denied: couldn't grab the accept mutex Date [alert] Child xxx returned a Fatal error... Apache is exiting! Date [emerg] (43)Identifier removed: couldn't grab the accept mutex
To fix this issue, edit ‘/usr/local/apache/conf/mod_ruid2.conf‘ and add the following line :
AcceptMutex posixsem
Restart httpd service and see how things are moving !