I keep being surprised how few people are aware of all the things they can use strace for. It's always one of the first debug tools I pull out, because it's usually available on the Linux systems I run, and it can be used to troubleshoot such a wide variety of ...
I was setting up Apache on OpenVZ earlier today, and ran into a problem with enabling SSL. Apache would refuse to start, and I'd see this in the error log:
[Sat May 24 07:48:10 2008] [warn] Init: PRNG still contains insufficient entropy! [Sat May 24 07:48:10 2008] [error] Init: ...
If you're using OpenVz, you owe it to yourself to take a look at /proc/user_beancounters every now and again. Just today at work we were having bizarre problems with one of the containers:
Everything would seemingly work fine. Then the load would spike from 0.something to 150+ in less than a ...