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How to find reason why linux froze or crashed ? (lemmy.ml)
submitted 7 months ago by to c/linux@lemmy.ml
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My mint froze and i had to force shitdown, is there a ctrl alt delete ?

How to find the reason it froze ?

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[–] 51 points 7 months ago (2 children)

As an alternative to forcing shitdown, you may want to try laxatives.

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    • [–] 25 points 7 months ago (8 children)

    There are a couple of things you can do. If it is frozen then try pressing ctrl+alt+1/2/3/4 to swith to a different terminal this will let you either restart your DE or reboot the system safely.

    As far as debugging it I would typically start with looking at journal logs journalctl -b-1 should show you logs from the last boot.

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  • [–] 11 points 7 months ago (7 children)

    Even with a frozen system you can often still ensure data is written to inspect on the next boot. You may have a key labeled SysRq which likely needs an Alt modifier to trigger.

    Alt+Shift+SysRq+s to sync data to disk. Alt+Shift+SysRq+u to unmount the disks. Alt+Shift+SysRq+b to reboot the system.

    Execute them in that order.

    This can help ensure the data about the mishap is written to disk so it can be inspected after the forced reboot. I also check the logs in /var/log but I suppose all of those are in journalctl too these days.

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  • [–] 6 points 7 months ago (1 child)

    I'm not sure that I would recommend a newer user use sysrq. It is a very powerful tool that you definitely should not be blindly following from a random internet post without knowing what each command does.

    In a truly frozen system then it can be good, but only as a final last resort. If the system can be unfrozen by other methods then that should be preferred instead.

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  • [–] 3 points 7 months ago

    Totally switch to a terminal first like you suggested and see if you can work your way from there. My suggestion goes after yours. Always try to fix the running system first.

    It's probably wise to check man pages and other introductory documentation for most system administration tasks. Even though they're super low-level, they are in my opinion better to send than just pulling the power plug.

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  • [–] 6 points 7 months ago (3 children)

    You just reminded me ... Before I really got into IT in my career I was at a job that still had a messenger for the internal staff. I set my status message in it to "Raising Skinny Elephants Is Utterly Boring."

    I got chastised and made to change it, because the message might offend ... Skinny elephants, I guess? I never got clarification on that.

    (The manager had no clue what it meant.)

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  • [–] 5 points 7 months ago (2 children)

    Seems weird that you'd sync before terminating and killing processes. I prefer "Raising Elephants Is So Utterly Boring". Although some distros only enable the S, U, B/O anyway.

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  • [–] 2 points 7 months ago

    I've always used the longer version that asks processes to stop, then kills them before syncing and umnounting the disk.

    REISUB: Reboot even if system utterly broken

    Also, SysRq is often Print Screen on modern keyboards.

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    • [–] 11 points 7 months ago (1 child)

    There is https://en.wikipedia.org/wiki/Magic_SysRq_key but I've had some hit and miss success in actually getting it to work.

    Normally I first try see if it is only the graphical interface that has crashed by pushing ctrl+alt+F1 or F2 or F3 to try and switch to another terminal. If I can switch, I log in and reboot or restart the window manager.

    I also try SSH into the machine if I have another of around.

    If I do reboot, then I use 'journalctl -b-1 -e' to see what happened at the time the system froze.

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    • [–] 5 points 7 months ago

    ctrl alt del used to do a graphics reset which often was all that was needed. ctrl alt f2 should put you in a terminal. If you had not done that I would give it a try and see if the whole system had crashed which would cause the terminal to not be responsive or if its just the grahics in which case you can login and reset the graphics.

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