Perhaps the greatest kernel compile option ever. Yeah umm I'm talking 'bout a linux kernel here. So you just recompiled your kernel with it or maybe it was there in the first place... anyway, it is very helpful when everything goes to crap and you can't seem to do anything.
Of course if your NumLock light won't change when you hit NumLock, you are prolly screwed. Most of this is all written up in linux/Documentation/sysrq.txt. Read that. Then if all has gone to hell on your system, and you really just wanna reboot do this and you won't see any fscking up.
Invoke the magic SysRq key with alt sysrq and then each of the following, in order and waiting for your disks to stop spinning between each:
E -- terminate all processes (SIGTERM)
I -- kills all processes (SIGKILL)
S -- syncs
U -- mounts fs's readonly
B -- reboots
There you go, system rebooted uptime lost, but who cares, right?
r and k are good keys for when a graphical (svgalib or X) crashes.
Like I said, read the sysrq.txt for the full details.
Oh yeah, I semi snarfled most of this from a /. comment attached to http://slashdot.org/articles/99/05/20/0239226.shtml by Dwonis. Thanks.