Today my Linux Mint Debian Edition LMDE laptop Lenovo Thinkpad T460P was frozen when turned off, at a black terminal screen where a lot had been going on but not coming to the end and turn off the system. I had been in hibernate state before, nothing I normally use, and when activating again it was not fully normal so I intended to turn off/restart.

I know the power off button should not be used on Linux if possible.

Today it worked with the reisub command: hold down ALT and SysRq and at the same time as those are still hold down, type r e i s u b very slowly, seconds in between.

  1. Hold down ALT + SysRq
  2. Type the keys r e i s u b, on at a time, in slow pace, still holding down ALT + SysRq
  3. Release ALT + SysRq (next step will start anyway, I think)
  4. Computer reboots

And yes, it is difficult to do this with only two hands, but managable. It workf for me, machine rebooted and work as normal again. Relief!

Note that I use my laptop with a full size external keyboard. Many laptops does not have any SysRq key on the keyboard. The function is available always or mostly, but it differs between brands and models how to activate SysRq when it does not have its own key. For example, several Thinkpad models incl T460p, the key combination FN + S activates the SysRq according to Lenovo support page.

I have a Lenovo Ideapad 100s, where I cannot find info, but this seems to be the way to manage SysRq:

  1. Hold down ALT + FN + Print Sc
  2. Release FN + Print Sc (still hold down ALT)
  3. Type the keys r e i s u b, on at a time, in slow pace
  4. Release ALT
  5. Lenovo Ideapad 100s reboots

This article describes what I did: Cleanly Restarting Your System. Use the Magic SysRq Key on Linux to Fix Frozen X Servers, Cleanly Reboot, and Run Other Low-Level Commands.

Also Wikipedia: Magic SysRq key.

You can also listen when I talk about this on Hacker Public Radio: hpr4137 :: I used reisub key sequence to reboot my frozen Linux computer. A frozen Linux computer can safely be rebooted with the reisub key sequence. Aired 11 June 2024.

Henrik Hemrin

29 May 2024

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