Panic on boot. How do I get a kernel dump.

Peter Jeremy peterjeremy at
Fri Apr 27 22:21:19 UTC 2007

On 2007-Apr-27 14:00:21 -0400, Kris Kennaway <kris at> wrote:
>On Fri, Apr 27, 2007 at 08:31:16AM -0700, Tom Cumming wrote:
>> One possibility is to hard code dumpdev in the kernel, then boot that
>> kernel.
>I don't know many different ways I can say "there is no way to do it".

I think Tom is saying that he needs to do something that _used_ to be
possible.  Normally the Project is careful to avoid regressions so
this was a surprise to me as well.  (It looks like it's demise wasn't
clearly spelt out at the time).

Since dumpdev is now intertwined with geom and the geom tasting is
quite late in the boot process, I agree that the current crashdump
code does not seem amenable to use early in the boot process.

Having a kernel crash before it reaches userland is not unheard of.
Whilst it may be possible to debug this using DDB or remote GDB in
some cases, I can think of two cases where this is not practical:
1) It is a production server that can't be left down for extended periods.
2) It is a remote system without remote console access.

Lets put the original question slightly differently:  How can the
kernel state be saved if the kernel crashes before it's possible to
invoke dumpon(8)?  IMHO, "there is no way to do it" is not a
satisfactory answer for the reasons above.

Peter Jeremy
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