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The first time my laptop froze, I used the Alt+SysRq REISUB and it worked.
Next time it happened - it didn't work.
I edited the 10-magic-sysrq.conf file's line kernel.sysrq = 176 (changed it to value 1).

I want to be sure that next time my laptop will freeze, the combination will work.. how do I check that Sysrq works?
(Shift + Alt (or) Alt Gr + SysRq didn't work, with and without Fn)
I run Ubuntu 14.04

2 Answers 2

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Press your key combination while tail-ing your /var/log/syslog file. In my case, if I press Alt-SysRq-m (memory dump, see the list here) you should have some message appearing. In my case:

Feb  5 16:04:14 pern kernel: [281437.665719] SysRq : This sysrq operation is disabled.
Feb  5 16:04:22 pern kernel: [281445.815216] SysRq : This sysrq operation is disabled.

So I know that the kernel is receiving the message. If it's authorized, you should have a complete memory statistics in output.

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  • To my disappointment, my computer have just froze again and the REISUB combination didn't work :(
    – Tzahi Leh
    Feb 6, 2016 at 14:37
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This might damage your system!

I am not an expert. This might be entirely unsafe. But what I did, was:

  1. Boot the computer - so that nothing very important would be working in the background.
  2. Go to another TTY. E.g. to go to tty4 you can press Ctrl+Alt+F4. You don't need to log in.
  3. Simply press the Magic SysRq keys you wish to test.
  4. You should now see the normal SysRq output. If there are any errors you can memorize or take a photo of them.
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  • What keys exactly should I try to test if it's working? May 5, 2023 at 0:08
  • 1
    These are your options. b is very easy to notice: Immediately reboot the system, without unmounting or syncing filesystems
    – Carolus
    May 8, 2023 at 19:19

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