If you ever encounter a system lockup in Ubuntu here’s a little trick you can use to safely restart your computer.
Hold down the Alt and PrtScn/SysRq keys at the same time and, keeping them held down, enter the following sequence of keys: R, E, I, S, U, B. Hold each key down for a second or so and don’t rush.
What it does is it allow Linux to take control of your system, requests politely that all processes close, forces all processes to close, flushes data to disk, unmounts your filesystems and reboots.
Here’s a couple of mnemonics: ”Raising Elephants Is So Utterly Boring” or “Reboot Even If System Utterly Broken”.
It’s extremely rare that this is necessary due to Linux’s stability but I’ve found I’ve needed this a couple of times recently (I suspect Google Chrome is the culprit) so I’m posting this here for easy future reference from my phone.