Mounting from ufs:/dev/ad2s1a failed with error 19.

[Trond Endrestøl]

On Thu, 30 Apr 2020 21:47+0200, Christoph Kukulies wrote:

> Fine, but where in the installation process would I have had a chance to decide for that option?
> Can I define UUID labels (is that GPT?) in the hindsight?

Your system uses MBR, hence the ad0s prefix.

UFS labels can be set while in singleuser mode, this is particular 
important for the root filesystem.

 1. Reboot to singleuser mode.
 2. Hit the enter key when asked about which shell to launch.
 3. tunefs -L root /dev/ad0s1a
 4. Ditto for the other *UFS* partitions. Consult your /etc/fstab.
 5. Verify the labels using dumpfs /dev/ad0s1a
 6. Reboot to multiuser mode.
 7. Duplicate the necessary lines in /etc/fstab.
 8. Comment out the original lines, in case you must revert.
 9. Change the duplicate lines to refer to /dev/ufs/root, etc.
10. Reboot to see if you have succeeded.
11. Remove the original lines in /etc/fstab, if desired.

I recall issues in the past using glabel(8) which stores the label in 
the last disk block (sector) of the partition. Hence the labeled 
device file should present a device which is one disk block shorter to 
avoid the label being overwritten. Maybe someone else can chime in on 
this.

I prefer GPT labels. See gpart(8), in particular
gpart modify -l label -i index diskdevice.

-- 
Trond.