We all love Ubuntu, right? Well there is times when the OS can lock up/freeze, preventing you from doing nothing else then a hard shutdown/reboot. You can shut off the computer by pressing the power button, or you can remove the power cord/battery if the button does not work.
In Linux (Ubuntu is what is focused on in this tutorial), you can use a simple set of keyboard presses all at one time to get the system to reboot. This is a kernel level reboot, and is considered a last resort to when the system becomes completely unresponsive, meaning that no interaction of any input devices is being recognized by the OS.
The keyboard shortcut is ALT + PrntScrn (Print Screen) + R + E + S + I + U + B. If the command does not work the first time, then you should try it one or two more times. The command should work. If it doesn't then the system (a: Seriously locked up and (b: The only option you have left is to remove power from the computer, losing all data in memory and potentially corrupting your hard drive.
Hope you all enjoyed this tutorial.