There you are, staring at a crashed Gnome session, CTRL-ALT-BKSPC does nothing. ALT-CTRL-F1 won’t bring you to a terminal where you could cd to /etc/init.d and restart gdm. In short, your choices seem to be limited to holding down the power button and chancing file system corruption or nothing.
But wait! There’s two more options that you may not have known about!
Here are two ways to first try and kill just the process on your current terminal (thus allowing you to get back into your machine and at least attempt a ’shutdown -h now’ command) and if that fails, to bring your machine down in a more graceful manner than a hard shutdown.
First, we’ll try and kill all the process on your current terminal. To do this, hold down the following keys -
ALT + SysReq + k
What the heck is a SysReq key? Look for it on your PrtSc or Print Screen key. The k in this instance stands for Kill.
If that doesn’t work for you, it’s time to take drastic action. You’ll now enter a series of keystrokes that will tell your computer to do some housekeeping before shutting down.
ALT + SysReq + r
This stands for Raw keyboard mode.
ALT + SysReq + s
This syncs the disk.
ALT + SysReq + e
This terminates all processes
ALT + SysReq + i
Kill’s all processes that weren’t terminated nicely.
ALT + SysReq + u
Remounts all filesystems as read only.
ALT + SysReq + b
That’s a heck of a lot better than simply holding down the power button and hoping everything works out okay.
How will you ever remember all those keystrokes? There is a long held mnemonic that makes it a bit easier:
Raising Skinny Elephants Is Utterly Boring - RSEIUB
You should use this method only if other methods (mentioned above) fail.
How to gracefully reboot your Ubuntu/Debian system if all else fails | ArsGeek