[Crash-utility] How do debug the kdump kernel using a Xen dump-core file?

[Cliff Wickman]

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 at sgi.com
(651) 683-3824