What I like to do in these cases is compile a kernel without DDB, but
configure enough swap space to have the machine take a dump when it
crashes.  Then, in the rc scripts, run savecore which preserves the crashed
image in /var/crash, or wherever you have enough space.  Then, savecore
logs the panic message, you can run ps, dmesg, gdb against the image at
your leisure and learn a lot without inconveniencing the user too terribly
much.  Note that even on Sparcs, where the dmesg buffer would get corrupted
in the dumped image under 1.3, I was able to get useful panic strings.
-Brian

On Oct 9,  1:09pm, Roger Brooks wrote:
} Subject: Re: Kernal panic woes
} On Fri, 9 Oct 1998, Christos Zoulas wrote:
} 
} >In article <Pine.SOL.3.96.981009121304.23059A-100000@uxa.liv.ac.uk> Dave.Tyson@liverpool.ac.uk (Dave Tyson) writes:
} >
} >>panic: trap
} >>#0  0x6 in ?? ()
} >>(gdb) where
} >>#0  0x6 in ?? ()
} >>#1  0xf01e5d3b in cpu_reboot ()
} >>#2  0xf013a949 in panic ()
} >>#3  0xf01ec5d6 in trap ()
} >>(gdb) q
} >>
} >>I have had a quick look at the source code around this this area, but it
} >>is not very enlightening. Any suggestions as to how to pin down this 
} >>problem would be appreciated. 
} >
} >
} >You are dying because of a panic, which is good. Unfortunately you are
} >rebooting immediately after a panic, so that you are not seeing the panic
} >message. In addition, your stack is trashed, so you don't see where panic
} >is being called from. I suggest that you compile a kernel with ddb, and
} >when it panic's you'll see the message in the console, and you'll be able
} >to print a complete backtrace. My suspicion is that you are running out
} >of some resource and you need to boost some parameter.
} 
} The problem is these machines are in user service, providing our site's
} web cache.  Having the system drop into ddb on panic is fine during the
} day when there's someone here to notice it, but if it happens overnight
} or at weekend we want the machine to reboot without intervention.  Is
} there any way we can build a kernel with ddb and then toggle the behaviour
} on panic (enter ddb or reboot) on the running system?  We can't really
} build two kernels (with and without ddb) and reboot twice daily!
} 
} 
} Roger
} 
} ------------------------------------------------------------------------------
} Roger Brooks (Systems Programmer),          |  Email: R.S.Brooks@liv.ac.uk
} Computing Services Dept,                    |  Tel:   +44 151 794 4441
} The University of Liverpool,                |  Fax:   +44 151 794 4442
} PO Box 147, Liverpool L69 3BX, UK           | 
} ------------------------------------------------------------------------------
} 
>-- End of excerpt from Roger Brooks