I am running a Turnkey Linux LAMP stack (based on Ubuntu). The server is hosting a relatively large WordPress installation with a pretty hefty amount of allocated RAM (on a dedicated machine). We get about half a million visitors a year, so it's not overwhelming.
And yet, sometime between every four hours and every four days, the server just stops serving pages. I've looked in the Apache logs, and all I've found are some known errors where certain graphic images are no longer available. I haven't found anything that seems to provide a clue why this is happening.
The machine itself doesn't fail, because I can connect in via Webmin and reboot. Once I reboot, it works fine -- again for a random amount of time.
So, where do I start trying to narrow down what's happening? As far as I can tell, the Apache and MySQL processes are still running. Just nothing's being service.
Any help would be much appreciated.