Discovered that xcache and xdebug are not compatible. For some reason, after trying to run them together php-fpm wouldn't start even though I had disabled xdebug. Disabling both xcache and xdebug has fixed the issue. Now I have to figure out how to get xcache working again... Posted at Nginx Forum: http://forum.nginx.org/read.php?2,223827,223832#msg-223832