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Old 02-10-2011, 12:42 PM
Cliff Wickman
 
Default How do debug the kdump kernel using a Xen dump-core file?

Hi Olaf,

On Thu, Feb 10, 2011 at 02:07:02PM +0100, Olaf Hering wrote:
>
> Hello,
>
> 'xm dump-core -L <domain>' generates a coredump of a Xen4 HVM guest, and
> crash is able to poke around in this coredump.
> Thanks for that.
>
> But: How can I use crash to debug the crash/kdump kernel itself?
> I did a 'echo c > /proc/sysrq-trigger' and want to look at the crash
> kernel, not the normal kernel.
>
> Olaf

You can make the crash kernel come all the way up to multi-user mode.
Then run crash. I haven't run crash under the crash kernel, but I don't
see why it wouldn't work.

I use this method with a SLES system:
edit /etc/sysconfig/kdump and set KDUMP_SAVEDIR to a
non-existing dir:
KDUMP_SAVEDIR="file:///fubar"
KDUMP_IMMEDIATE_REBOOT="no"

Or this seems to work with a RHEL6 system:
- edit /etc/init.d/kdump and comment out the makedumpfile and restart
lines; just make it exit
- modify script /sbin/mkdumprd so that it does not save a
dump, but goes to user mode:
2429,2430c2429,2432
< emit " $CORE_COLLECTOR /proc/vmcore $VMCORE-incomplete...
> emit "# $CORE_COLLECTOR /proc/vmcore
> $VMCORE-incomplete...
---
< emit " exitcode=$?"
> emit " exitcode=1"
2444c2446,2448
< emit " $FINAL_ACTION"
> emit " echo bye"
and /etc/init.d/kdump to not call save_core in the crash kernel:
start)
if [ -s /proc/vmcoreXXX ]; then
save_core
)

-Cliff
--
Cliff Wickman
SGI
cpw@sgi.com
(651) 683-3824

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