[Pkg-xen-devel] how to get debugging output from dom0 kernel

[lee]

Ian Campbell <ijc at hellion.org.uk> writes:

> On Sun, 2014-06-15 at 13:35 +0200, lee wrote:
>> Ian Campbell <ijc at hellion.org.uk> writes:
>> 
>> > On Sun, 2014-06-15 at 11:03 +0200, lee wrote:
>> >> Hi,
>> >> 
>> >> how could I get better debugging output from the dom0 kernel?
>> >
>> > Either configure a serial console [0] or add "noreboot" to your
>> > *hypervisor* command line, so you can see (and perhaps
>> > transcribe/photograph) the crash before manually rebooting.
>> 
>> The server isn't rebooting automatically, it only gets stuck.  I still
>> have a monitor connected to it, so I can see what's printed to the
>> console.  But the output is scrolled off screen by subsequent messages
>> so that it's gone by the time I notice that it hangs.
>> 
>> If there was a way to disable the subsequent messages, I could take a
>> picture.  Perhaps I can get output from a serial console if I manage to
>> set that up ... or maybe I can actually make it crash instead of having
>> to wait ...
>
> Serial console would be best. I think the Linux kernel also has a panic
> on crash option somewhere, perhaps oops=panic, but it depends rather
> what form the initial error takes.

That's the most difficult option --- the server has a management card
which apparently is able to show you console output in a web browser,
but that seems to require some java plugin to work, and since nothing
java ever works, I haven't been able to use that --- plus I had to get
another network cable first.

Last time it crashed I looked, but only an empty screen was displayed on
the console.  So I upgraded to a 3.14 kernel from backports, and it's
running over 24 hours yet.

It might be a good idea to upgrade the kernel for stable or at least to
place an info into the description that if it crashes, ppl can try a
backports kernel.

> I suppose there are also various software monitoring solutions which
> would alert you to something odd in the dom0 dmesg e.g. via email.

That could be useful for normal operation.  When the kernel has crashed,
such software probably can't do anything anymore.


-- 
Knowledge is volatile and fluid.  Software is power.