Debugging kernel panics

[Greg 'groggy' Lehey]

On Tuesday,  9 September 2003 at  3:46:07 -0400, Michael Reynolds wrote:
> I've recently cvsup'd from 4.8-STABLE to 4.9-PRERELEASE.  After a
> reboot, my machine's kernel panics at the initialization of the xl1
> device (a 3com nic).  I've checked out the FAQ on the site, under
> advanced topics, regarding kernel panics, and read the relevant man
> pages.  I have 2 swap partitions, ad0s1b, and ad2s1b.  I have set
> dumpdev to "ad2s1b" in /etc/rc.conf and /boot/loader.conf.  I've also
> built a debug kernel.  However, it appears a kernel core is not being
> dumped on panic.  I've manually executed savecore, with force option,
> and it wrote a 0 byte vmcore.

That probably means that there wasn't a dump there.  You normally
don't need to force it.

> Is there anywhere else I need to specify the dump device?

No, that's all.

> Do I need to specify the full path instead of just the device?

Ah, yes, of course.  There's no way for the dump routines to guess a
path.  Try /dev/ad2s1b.

> I've not had a kernel panic before, so I'm pretty much a newbie when
> it comes to that aspect.  I have no custom code added to the kernel.
> Any help will be *greatly* appreciated.

A couple of other points:

1.  Your swap partition needs to be at least fractionally larger than
    your real memory.  The dump routines write a dump and a header.
2.  You need enough space for the dump on /var/crash.  Otherwise it
    won't save the dump.

Greg
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