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Date: Fri, 26 Dec 2008 17:34:38 +0000
From: Kris Kennaway <kris@FreeBSD.org>
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To: Glen Barber <glen.j.barber@gmail.com>
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Cc: freebsd-stable <freebsd-stable@freebsd.org>
Subject: Re: Kernel Trap during installworld caused unrecoverable system
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Glen Barber wrote:
> Hi folks.
> 
> I was unfortunate enough to encounter a kernel trap in single user
> mode yesterday when upgrading from 7.1-RC1 to -RC2 using the typical
> build/install world.
> 
> I'm still not sure what caused the trap, as the system was rebooting
> when I saw the screen.  As one would expect, this led to an
> irrecoverable system; the system would automatically drop me into
> single user mode, as it could only mount the root directory; /bin/sh
> and /bin/csh would not work (had to use /restore/csh for the minimal
> digging I actually could do).
> 
> So, now to the question.  Given I could not mount anything other than
> /, would there have been any way for me to gather debugging
> information on what caused this failure?  (FWIW, I am certain it is
> not a hardware failure.)

You can proceed recovering the system using the tools in /rescue, and 
once you have shared libraries working again, run savecore to save the 
crashdump (assuming one was made).

Kris