...and there came the day the Linux stood still.

Damn you Linux!
And it gets worser..
Damn you Ubuntu!
Half a day lost - for what? Don't know. I know what happened. A machine running Ubuntu 64 bit Server (that had worked fine for over 8 months) suddently stopped booting into gdm.
On login to any user, it woulds state "/dev/null no permissions". WTF?
See, this is exactly why linux (written with a lower case L on purpose, didn't deserve the capital one today!) sucks. When something goes wrong - it NEVER does, really, but when it happens - its almost a total disaster. Mainly for two reasons.

1. The system usually is totally or partially unusable
2. Finding out what happened takes half a time of your life
3. 20 years of development and noone cared doing a proper, centralized log viewer interface - you know what, f*ck you.

Well the third reason came out of my hearth, just had to log it. Sorry dudes.
So what happened? Apparently, some "obscure" thing mixed up the /lib/lbs/init-functions file, which ended up being empty. This in turn caused the (all) services to exit with log_daemon_msg messages, causing services who invoked them to think they failed.
Which translates in a clean boot in the most proper way, as in no services started. Not even ifconfig for configuring the network interfaces for an example.

Well, luckily that "obscure" thing was kind enough to take a backup of the init-functions before erasing the contents. Which btw excludes Hard Disk crashes (and shuts the mouth to all of you I-know-better out there)who are not even as half as nice to make a backup before taking action.
Once restored, the system seems to work fine (so far).
But what caused that problem? No one knows, not even Google....