Re: debugging 15.0-RELEASE kernel on 15.0p3?

On 2/17/26 11:41, Alan Somers wrote:
> On Tue, Feb 17, 2026 at 12:37 PM Michael W. Lucas <[email protected]> wrote:
>> This host didn't have kernel debug symbols. I went to install them and
>> discovered my host needed updates. Thoughtlessly, I grabbed the new
>> kernel and the new symbols.
>>
>> Oops. You can't debug a 15.0 kernel on 15.0p3.
>>
>> bucket/var/crash;kgdb -n 0
>> kgdb: couldn't find a suitable kernel image
>>
>> I have a 15.0 boot environment I could boot into, if there's a way to
>> install the debugging symbols? Or is there a way to pull the old
>> kernel and debug symbols down on the current BE?
>>
>> On dch's advice I tried setting the pkg.conf URL:
>>    url:
>> "pkg+https://cloudfront.aws.pkgbase.freebsd.org/FreeBSD:15:amd64/base_release_
>> 0/"
>> but got:
>> pkg: No SRV record found for the repo 'FreeBSD-base'

That isn't going to work because pkg+https says "look up SRV records" and the
cloudfront.aws.pkgbase.freebsd.org endpoint is *what the SRV record points
at*.  You could have used pkg+https://pkg.freebsd.org/, but that wasn't going
to work anyway since the repo will give you the latest packages (aka the -p3
kernel).

The older packages are actually still there, but there's no way for you to
find them.

> You can probably install the symbols from the DVD image.  They're in
> the kernel-dbg.txz dist set.  That should work for you, since your
> crash happened in 15.0.  But the same technique wouldn't work if you
> had crashed at, say, 15.0-p1.

The DVD image is the way to go.  Either from kernel-dbg.txz or from the
pkgbase repo on the DVD image.  But as Alan notes, this only works because
you crashed on the original release.

We should probably consider creating a separate stash of kernel debug packages
so people can fetch a not-most-recent version if needed.  I never thought
about this until now.

Oh, a third option is to boot up an EC2 15.0-RELEASE-p1 image ("base" or
"cloud-init"; "small" doesn't have debug symbols).  But I'm guessing you'd
prefer to look at your panic locally.

-- 
Colin Percival
FreeBSD Release Engineering Lead & EC2 platform maintainer
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid