How to reboot hung system

It happens that the system freezes. Either X does not come out of the swap, or a process has eaten all the memory and the keyboard handler cannot get control, or recognize that the browser is slowly leaking the roof, well, in general, do nothing except reboot.

But how to make it so as not to damage the hairstyle of the file system. Let us resort to the so-called magical nuclear button, namely the combination Alt-SysRq (also known as PrintScreen) with different letters. We need these in this order, given that we have a qwerty keyboard:

Alt-Sysrq- R switch the keyboard to XLATE mode (take control of the X)
Alt-Sysrq- E send a strong hello to all processes, except for Inita, that is, SIGTERM
Alt-Sysrq- I send final greetings to all processes, except for Inita, that is, SIGKILL
Alt-Sysrq- S sync. For followers of the old school: click twice :)
Alt-Sysrq- U remount all file systems in read-only
Alt-Sysrq- B start download
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It is said that this sequence (Alt-SysRq- REISUB ) can be remembered as the word BUSIER, on the contrary. From myself, you can add that if you want to refresh this brief mnemonic in your head, you can press Alt-SysRq-H on the console, and a brief reference will be issued. For those who are not sure where he has the console: press Ctrl-Alt-F1.