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I've followed the directions here on the Ubuntu help wiki for my 12.04.2 Ubuntu Server running in VMware Fusion 5, and everything looks good, so I do a echo c > /proc/sysrq-trigger as root. It panics the kernel as expected, and then hangs after printing out a bunch of stack traces.

I waited a few minutes to make sure any writes to disk (for the crash dump) finished, and I restarted the VM. When I log in again, ls /var/crash shows no files! Any idea how to get it to work, or whether it works at all?

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2 Answers 2

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The reason why this doesn't work properly has been well documented for over three or so years now: see this page of the Ubuntu wiki

On systems with <= 2G RAM we won't reserve enough memory for the crash kernel's initrd to fit. That will cause the crash-kernel to panic.

See also these bug reports for reference #785394 and #1235616

Workaround:

To fix this issue set

GRUB_CMDLINE_LINUX="crashkernel=128M"

in /etc/default/grub. n.b.: You cannot put this option into GRUB_CMDLINE_DEFAULT, because the the setting in /etc/grub.d/10_linux takes precedence over that.

To "permanently" fix the issue, edit `/etc/grub.d/10_linux and change the line

GRUB_CMDLINE_EXTRA="$GRUB_CMDLINE_EXTRA crashkernel=384M-2G:64M,2G-:128M"

to

GRUB_CMDLINE_EXTRA="$GRUB_CMDLINE_EXTRA crashkernel=128M"
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  • While this doesn't answer the question, I'll let it go because it satisfies the "partial answer" rule.
    – jokerdino ♦
    Oct 4, 2013 at 16:07
  • @jokerdino it became an answer :)
    – Zanna ♦
    Jun 25, 2018 at 5:47
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The problem might be your RAM is too low. It should be greater than 2GB otherwise you have to change GRUB parameters to accept crashkernel=128M and check 

cat /sys/kernel/kexec_crash_loaded

It should be 1.

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