kdump-tools does not start a shell with the given option

[Javier]

From the Ubuntu manpage for kdump-tools (https://manpages.ubuntu.com/manpages/noble/en/man5/kdump-tools.5.html):

This option starts a shell if kdump-tools cannot save the vmcore file:
              KDUMP_FAIL_CMD="/bin/bash; reboot -f"

But that does not seem to work.

I forced kdump-tools to fail by passing an invalid file to save the dumps, and I triggered a panic with 'echo c > /proc/sysrq-trigger'.

The systems boots the kdump kernel, and then I see the following messages on the screen:

* kdump-tools: failed to save vmcore in /var/crash/no_writtable/202407010739
/etc/init.d/kdump-tools: 36: /bin/bash; : not found
[ OK ] Finished kdump-tools-dump.service - Kernel crash dump capture service.

The system freezes, and only a power cycle can bring the system up again.

I have also tried with KDUMP_FAIL_CMD="/bin/bash", but the system freezes anyway without any error message. A single 'echo XYZ' displays "XYZ", and the system freezes afterwards.

If no KDUMP_FAIL_CMD is set, kdump-tools works normally as long as it finds a valid path to write the dump, so the tool itself is alright.

Is the example given in the manpage wrong? If so, how can I start a shell if the vmcore file cannot be saved?

Tested with Ubuntu 23.10, kernel 6.5.0.42-generic, kdump-tools installed via apt. Links and options for vmlinuz and initrd.img have not been edited (standard location after installation: /var/lib/kdump/{vmlinuz,inird.img}).