Sometimes when a Linux system is unresponsive it seems like your only option is to hold down the power button.
Follow these key combos for a less risky reboot.
Hold Down Alt + SysRq and press R (raw keyboard mode) S (syncs disks) E (terminates all processes) I (kills the stragglers) U (read-only remount file-systems) B (reboots)
Give it lots of time to Sync the Disks and do it one more time after killing the processes to play it safe.
There she be. Careful, it’s a lot of fun.
Reboot System Even If Utterly Broken