> Wasn't there a whole seqence of ctrl-alt-letter things to gradually
> shut down the entire system, layer by layer? Antybody still know
> these, and are they still there?

Ah yes, the "magic keys."

Holding down Alt and SysRq (which is the Print Screen key) while slowly
typing REISUB will get you safely restarted. REISUO will do a shutdown
rather than a restart.

I don't know about Debian (because currently not installed), but in Ubuntu
this useful feature is disabled by default. It can be turned on easily
enough. As root open file /etc/sysctl.d/10-magic-sysrq.conf and comment out
or modify the line that says:

kernel.sysrq = 176

(note: might not be "176")

and change it to:

kernel.sysrq = 1

Reboot, and you're done.

Another ctrl-alt combination that's disabled in Ubuntu is the ability of
ctrl-alt-backspace to break out of X and take you to the login prompt. You
can enable it by adding the following line to .bashrc and .bash_profile:

/usr/bin/setxkbmap -option terminate:ctrl_alt_bksp

cheers,
Robert