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Date: Mon, 28 Oct 2019 12:22:55 -0700
From: Kees Cook <>
To: Muni Sekhar <>
Subject: Re: How to get the crash dump if system hangs?

On Fri, Oct 25, 2019 at 07:40:58AM +0530, Muni Sekhar wrote:
> After loading the ramoops module, I see it generates dmesg and console logs.


> I’ve a actual test case where my system gets frozen  so have no
> software control. I executed this test case and as expected my system
> has frozen and recovered it by powering it on(cold boot?) and then
> loaded the ramoops but this time no files present in /sys/fs/pstore.

I wonder if you could use a hardware watchdog driver of some kind to
trigger the soft reboot?

> If you restart a PC in cold(hard) boot, is it possible to see the RAM
> memory(previous boot) still? I really I don’t know how it works.

It depends a lot on your chipset and RAM. It sounds like your system
very quickly wipes its RAM contents on a cold reset.

> So, is there a  way to automatically reboot the Linux system when it
> freezes? I set “kernel.softlockup_panic = 1, kernel.unknown_nmi_panic
> = 1, kernel.softlockup_all_cpu_backtrace = 1, kernel.panic = 1,
> kernel.panic_on_io_nmi = 1, kernel.panic_on_oops = 1,
> kernel.panic_on_stackoverflow = 1, kernel.panic_on_unrecovered_nmi =
> 1”, but it does not helped to reboot when it freezes.

See if Documentation/nmi_watchdog.txt helps?

Good luck!

Kees Cook

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