kernel dump

[Michael Havens]

thank you so much Jerry. That was quite helpful. made me realize that I was
getting in way over my head! So now I am reading one of the resources
<https://www.kernel.org/doc/Documentation/kdump/kdump.txt>.

On Thu, Dec 10, 2015 at 6:30 PM, Jerry Snitselaar <dev at snitselaar.org>
wrote:

> 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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-- 
:-)~MIKE~(-:
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