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Date: Thu, 26 Apr 2007 18:37:42 -0700
From: Steve Kargl <sgk@troutmask.apl.washington.edu>
To: freebsd-current@freebsd.org
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Subject: Re: Panic on boot. How do I get a kernel dump.
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On Fri, Apr 27, 2007 at 09:24:02AM +0800, Wilkinson, Alex wrote:
>     0n Thu, Apr 26, 2007 at 03:35:15PM -0700, Tom Cumming wrote: 
> 
>>The problem is not getting it to panic, the problem is getting it to save
>>core after the panic. I can find no way to configure the dump device before
>>I boot, only after the OS is up. This means a panic during boot will not
>>dump core because the dump device is not configured.
> 
> Boot off of a good kernel and:
> 
>    # boot -s
>    # fsck -p
>    # mount /var
>    # savecore /kernel.broken /var/crash
> 
>  -aW
> 

Re-read the text that you quoted.  Tom doesn't have 
dumpdev set, so there is no core for savecore to
retrieve.  ISTR, that one could set dumpdev in the
loader.  At the loader prompt, do 

set dumpdev="/dev/ad0s2b"  

-- 
Steve