On 10/10/07, Jacob Yocom-Piatt <jy-p@fixedpointgroup.com> wrote:
quoted text
> had a problem with the / partition getting full (105%) on a fileserver
> here and then rebooted it. after rebooting the "ERR M" line came up
> immediately after the "drive 0 partition 3" message that is normally
> followed by the boot prompt. this is an amd64 4.1-release machine and i
> can't account for this behavior aside from the overfull state of the /
> partition during shutdown.
>
> so i booted off a USB drive (i386), mounted / from the other disk and
> cleared off the stuff that had eaten all the space. rebooted and got the
> ERR M again, so apparently something became hosed from the first time it
> was shutdown with an overfull /.
>
> got an amd64 install onto the USB drive so i could attempt booting /bsd
> from the "hosed" drive. at the boot prompt did a "boot hd1a:/bsd" and
> the machine is running, albeit using a USB drive to boot the kernel from
> hd1.
>
> have gotten the ERR M message before and recognize it indicates a bad
> magic number but am clueless as to how to fix it. clues appreciated
> here. find a link to the dmesg below.
>
> cheers,
> jake
>
> dmesg - http://marc.info/?l=openbsd-misc&m=118141026830100&w=2
>

http://archives.neohapsis.com/archives/openbsd/2004-09/1593.html
suggests that your boot(8) is corrupt. Running installboot(8) should
fix it. That means something like:

           # cp /usr/mdec/boot /boot
           # /usr/mdec/installboot -n -v /boot /usr/mdec/biosboot wd0

-Nick