How can i discover Debian Linux power-cycling reason (crash)?

[postcd]

My computer

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System:
  Kernel: 5.10.0-32-amd64 arch: x86_64 bits: 64 compiler: gcc v: 10.2.1
    parameters: BOOT_IMAGE=/vmlinuz-5.10.0-32-amd64 root=/dev/mapper/hostname--vg-root
    ro quiet crashkernel=384M-:128M
  Desktop: KDE Plasma v: 5.27.5 tk: Qt v: 5.15.8 wm: kwin_x11 vt: 7 dm: SDDM
    Distro: Debian GNU/Linux 12 (bookworm)
    10% free space.

suddenly power cycled (command "last -x|head" shows it as a " - crash (01:46)") so I have listed current and previous journal boots: sudo journalctl --list-boots
Then under previous boot displayed as boot -1 in previous command output, I have listed its most recent journal entries: sudo journalctl -b -1 -e

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Oct 04 08:16:32 plasmashell[2172139]: [2024-10-04 08:16:32.262] [   ] [debug] autosave: no needs to save file

(that has been last journal entry under that boot, after which reset happened. Before this entry there has been a silence for 12 seconds.)

running same command with "-k" (kernel messages) parameter (sudo journalctl -b -1 -e -k) does not show any log entries at that time.

I suspect memory issues/leak, since the memory was high incl. zram swap due to qbittorrent 5.0.0 (AppImage) has been using many gigabytes of swap.

Is there any more commands to run or to enable space efficient logging (to be prepared for the next crash of this kind), or if the cause is full memory (or power surge/faulty PSU?), no log can help? I am using single swap (ram based swap - zram) device.

[Aki]

Hello,

Overloaded operating systems usually don't restart through power-cycling. If overloaded, traces are in systems logs (i.e. out of memory [OOM] killer logs).

If you installed kdump-tools package and enabled/started the kdump.service, you may find a kernel core dump and backtraces in /var/log/crash after a kernel crash; see previous discussion:

• Help with diagnosing an OS freeze

If there's noting in logs, it's most likely due to a hardware (CPU / motherboard / RAM / PSU) problem.

[stevepusser]

Have you tried the default Debian Bookworm 6.1 kernel instead of the nonstandard 5.10 you are running?

[Aki]

Moved to "General Questions".