Have you ever wondered of what use the SysRq key is?
While working on my dual monitor setup, I tried several paths that led to an unresponsive X session (black screen). Ctrl+Alt+[1-6] didn’t work; Ctrl+Alt+Backspace didn’t work; so I did a hard reboot (and after unplugging a monitor so that I could get back into X, I set my default runlevel to 3 in /etc/inittab till I could figure out what was going on!)
While researching, I stumbled upon a post in a forum for Ubuntu users where someone suggested holding down Alt+SysRq and typing S, U, B (sync all mounted filesystems, remount filesystems readonly, reboot). Next time I had X in an unresponsive state, I tried it. What do you know, it worked!
Turns out it’s the Magic SysRq Key feature of the Linux kernel.
I don’t think my wife would appreciate the beauty of this magic key combination (she remains unconvinced about the amazing utility of Ctrl+Shift+Alt+PgDn for shutting down the computer from an X session without prompts :) , but for a keyboard shortcut connoisseur like me it was a fun find.