Every once in a while, my web server slows so significantly, it seems locked up. Can't SSH in, no sites being served. It's a VPS that started out as Debian 5 which I upgraded to testing (squeeze). It's a typical LAMP set-up with the sole purpose of running a couple of wordpress sites. One time when it locked up, I got to one of the sites, but it was wordpress complaining it couldn't establish a database connection. So it seemed as if something was really chewing up the CPU and mysqld either timed out, or possibly failed and couldn't restart. But since I couldn't SSH in I feel more inclined to attribute it to CPU. But the only processes running now, aside from OS and kernel stuff:

• apache
• mysqld
• python (for fail2ban)
• sshd
• exim4

It has 512M of RAM and 1.5 GB of swap. Every time I check on it, it has plenty of free memory and is using virtually no swap (usually 2-3M). And since I am running fail2ban I don't think I'm getting ddosed.

I did find this in my logwatch email this morning (it locked up late last night, when there would have been very little traffic):

6 Time(s):  [<ffffffff810a0ebc>] ? oom_kill_process+0x7e/0x23d
6 Time(s):  [<ffffffff810a1505>] ? __out_of_memory+0x12a/0x141
6 Time(s):  [<ffffffff810a1586>] ? out_of_memory+0x6a/0x94

I didn't find anything else suspicious. It can't be my provider's host because I can SSH in and restart the VM, and everything seems fine.

Anybody know which logs I should start poring through to find the core of my problem?

Thanks guys.