kernel dump

[Jerry Snitselaar]

On Thu Dec 10 15, Michael Havens wrote:
>   I want to see why my kernel panics (if it does) so I was lead to:
>   [1]https://help.ubuntu.com/lts/serverguide/kernel-crash-dump.html
>   sudo cat /etc/default/kdump-tools>> USE_KDUMP=1
>   Will the above line append USE_KDUMP=1 to kdump-tools.
>   --
>   :-)~MIKE~(-:
>
>References
>
>   1. https://help.ubuntu.com/lts/serverguide/kernel-crash-dump.html

I've never played with it on Ubuntu.

You will need the crashkernel parameter on the boot line so memory
gets set aside to the kdump kernel memory image.

Also you will need to reboot, so it builds the image if you haven't
already done so (according to that page, Red Hat/Fedora does the same
thing).

You will probably need to install debug symbols for the kernel in
question.  Not sure how that is done for Ubuntu.

It doesn't look like it explains it on that page, but look to see if
there is a kdump.conf file in /etc, that will probably need to be
modified to suit your system.

Once you have it up and running, when the system panics it will
jump to the kdump kernel, bring that up, harvest an image of the
memory, then reboot the system and come up again on the regular
kernel.

Then you would go to /var/crash or wherever it is configured to
place the vmcore file, and then:

crash /boot/System-map-for-kernel /lib/modules/debug/lib/modules/kernel-rel/vmlinux vmcore

The vmlinux part would be whatever location it installed the kernel image which still has
debug symbols not stripped.

Some commands:

bt       - prints backtrace of the current process
bt -a    - prints backtrace for processes on all cpus
bt -f    - prints the contents of the stack with the backtrace

help     - will list available commands and help command, will print
           out detailed help for the commands.

log      - dumps the in memory system log (what you would normally see
           with dmesg command)

set #    - set focus to certain pid
set -c # - set focus to certain cpu 

dis function-name - provides disassembled code for the function given

mod      - load symbols for a module

rd       - read contents of memory
struct   - display a struct, (with address provided as well dumps out
           formatted struct with values)


Unless you are familiar with kernel internals and assembly code, what
you'll probably want is to:

set scroll off
log

And look at the end of the log to find the message where it paniced,
and post those contents somewhere. If it is a distro kernel your best
bet will be contacting those folks.

Jerry

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