Magically reboot your frozen Linux machine with the keyboard! 🧙

Sometimes, my Ubuntu machine tends to freeze up and I would be unable to restart or shut it down. I’ve always just held the power button until it is forcibly shut down, but I felt it has always been rather harmful. So, I’ve set about looking for a better way, and I found out about the magic REISUB key. Basically, it goes like this:

Hold the Alt and SysRq keys, then slowly type out R E I S U B.

Found the original article over here, but it simply says how to do it, without explaining, so I dug deeper.

This stack exchange answer here provides a good answer:

  • R - switches keyboard (raw) mode to XLATE mode, short for translate mode.

  • E - gracefully terminates all running programs by sending SIGTERM signals to all processes except init. SIGTERM gives processes a chance to clean up and free up their resources, save data, etc.

  • I - forcibly kills all running programs. Basically E, but for those processes that refuses to shut down. Best if you wait a bit before pressing this button for E to gracefully shut down processes.

  • S - syncs all disks and flushes their caches, so that cached data can be written without losing data.

  • U - unmounts all disks, then remounts them as read-only. Read-only as a safety measure.

  • B - reboots the system. Like, a hard reset similar to holding the power button.

However…

On Ubuntu (which is the one I use, not sure about other distros), R, E, and I are disabled.

And…

If your intention is to simply shut down the PC without rebooting, replace B with O, which is the key for shutdown.

More details here (Wikipedia’s Magic SysRq key). 🧙🧙