As you may have noticed (but probably not), my server is really very, very unstable and seemingly randomly hangs. The problems started about last Sunday evening.
At first I thought an update was causing the problems (although I've never seen a Linux server completely hanging because of user space software), but that doesn't seem to be the case. Looking at statistical data about my system like CPU, memory, disk, network usage and temperature sensor information neither revealed any clues. Finally, when yesterday the serial port (that is being used to communicate with an old, but just fine APC UPS) just stopped working (but after restarting the server started working again) and also seeing strange kernel errors in syslog, it hit me it must be hardware issues and in this case most probably the motherboard.
Sending the motherboard back for repairs and then having to wait for probably weeks isn't an option, so today I ordered a new motherboard (the same model, so hopefully this instability issue after less than a year isn't a symptom of structurally using sub-par components) and this motherboard is expected to arrive in a few days' time. It will probably be next week the server is running stably again, I hope, but for now, it's sadly a question of keeping an eye on the server and switching it off and on again (just like Roy from The IT Crowd) when it hangs.