How to Restart a Unresponsive Linux System with Reisub

It may sometime happen that our Linux system hangs completely and the only option available is to shut down the system via the power button.

The power button to reboot could cause a problem if your hard drive is still being written to, and usually causes more problems than it solves. The Linux kernel includes a secret method of restarting your PC

 * Hold down the Alt and SysRq (Print Screen) keys.
 * While holding those down, type the following in order: REISUB

Alt + PrintScreen + r + s + e + i + u + b

 * With above key combination your frozen Linux system will go for a reboot.

Here is what the individual keys do in that sequence
R:Switch the keyboard from raw mode to XLATE mode
E:Send the SIGTERM signal to all processes except init
 I:Send the SIGKILL signal to all processes except init
S:Sync all mounted filesystems
U:Remount all mounted filesystems in read-only mode
B:Immediately reboot the system, without unmounting partitions or syncing