This is the classic sequence for the SysRq (System Request) magic keys on Linux!
When a Linux system completely freezes, typing Alt + PrtSc and then sequentially pressing R, E, S, U, B safely reboots the computer without damaging the hard drive.
Here is what each letter in that specific sequence does:
- R (Raw): Takes keyboard control back from the X server.
- E (Terminate): Sends the SIGTERM signal to all processes, asking them to shut down gracefully.
- S (Sync): Flushes all unsaved data from memory to the hard disk to prevent data loss.
- U (Unmount): Remounts all file systems as “read-only” so they cannot be corrupted.
- B (Boot): Instantly reboots the computer.
(Note: The full traditional mnemonic is actually REISUB—”Reboot Even If System Utterly Broken”—which includes the letter I to kill remaining processes before syncing).
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