"Cannot find file system superblock" error - how to recover?

[Scott I. Remick]

--- Sergey 'DoubleF' Zaharchenko <doublef at tele-kom.ru> wrote:
> I think you already have a copy (the data at offset 32 seems to be it).
> If you want, do a
> 
> # dd if=/dev/ad6s1 skip=16 count=16 of=/some/file

ok, done. Is there a way to use fsck_ufs -b now to fix this? Or is that
premature? And if I remember correctly, that doesn't actually APPLY the
alternate superblock... it just allows fsck to run while utilizing an
alternate one. So we need to use some sort of dd command to copy it to the
proper location, correct?

> Please tell me everything what you tried to use to mount/fsck the drive
> (and the results, of course).

Well, my memory is sketchy so I don't know how much use it'd be. But I was
saving a file to /data (ad6) when the system hung. Then it rebooted on its
own. Of course fsck ran on bootup but it gave up and told me I had to run it
manually. When I did (I don't remember any parameters I specifically used,
if any) I got:

/dev/ad6s1c
Cannot find file system superblock
/dev/ad6s1c: NOT LABELED AS A BSD FILE SYSTEM

I remember there being some of the other common message for little things
that you just tell it to go ahead and fix. But the above error was a brick
wall and would keep me from going multi-user. Ultimately I had to
comment-out the line in fstab:

#/dev/ad6s1c            /data           ufs     rw              2       2

So I could at least boot. And that's the way I've been ever since.

Trying to mount it now gives:

su-2.05b# mount -r /dev/ad6s1c /data
mount: /dev/ad6s1c on /data: incorrect super block

And so we stand.

> Try booting from a 4.x floppy and doing it all over again... The FS is
> UFS1, isn't it?

Ummm... doing what all over again? Wipe the disk and redo the partitions? I
hope we're not quite there yet. How does using 4.x give me an advantage over
5.1? I'm not clear on that part.