no clean unmount after shutdown -r (one disk, no RAID)

[Petar Bogdanovic <petar%smokva.net@localhost>]

Hi,

one of our systems leaves dirty file systems behind when rebooted
with shutdown -r:

# dmesg | tail
        wd0: drive supports 16-sector PIO transfers, LBA48 addressing
        wd0: 232 GB, 484521 cyl, 16 head, 63 sec, 512 bytes/sect x 488397168 
sectors
        wd0: 32-bit data port
        wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
        wd0(piixide1:0:0): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133) 
(using DMA)
        boot device: wd0
        root on md0a dumps on md0b
        root file system type: ffs
        /dev/wd0a: file system not clean (fs_clean=1); please fsck(8)
        /dev/wd0a: lost blocks 0 files 0

# cat /etc/fstab
        /dev/md0a   /       ffs     rw
        /dev/wd0a   /boot   ffs     ro
        tmpfs       /tmp    tmpfs   rw,-s64M,-m1777
        kern        /kern   kernfs  rw
        tmpfs       /var    tmpfs   rw,-s64M,-m0755
        tmpfs       /usr    tmpfs   rw,-s384M,-m0755
        /dev/wd0b   /opt    ffs     rw

# mount | sort
        /dev/md0a on / type ffs (local)
        /dev/wd0a on /boot type ffs (read-only, local)
        /dev/wd0b on /opt type ffs (local)
        kernfs on /kern type kernfs (local)
        tmpfs on /tmp type tmpfs (local)
        tmpfs on /usr type tmpfs (local)
        tmpfs on /var type tmpfs (local)

there is no RAIDframe configured and wd0a aka /boot is never mounted rw,
except approx. once a month when being updated through rsync.  Also the
dirty fs is not always the one on wd0a. Sometimes it's wd0b (mountpoint
/opt)---only used by syslogd, postfix and a milter.

Regarding our configuration:  We use a slightly modified mountcritlocal
where we added some lines to mountcritlocal_start().  Also we added the
following two lines to our rc.conf:

        critical_filesystems_local="$critical_filesystems_remote /boot /usr 
/var /opt "
        critical_filesystems_remote=""

The machine is miles away from my keyboard so unfortunately I can't
sneak a peek at the console.  Besides that, I'm a bit out of ideas..

Thanks for hints and pointers of any kind,

                Petar Bogdanovic