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

[Malcolm Kay]

On Wed, 7 Jan 2004 06:09, Scott I. Remick wrote:
> --- 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
>

This is true. That partition is labeled as unused.
I believe you should be trying to mount /dev/ad6s1e.

> 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
>

Certainly wrong in 4.x, I suspect also wrong in 5.x.
Do you have a line mounting ad4s1c for the other disk?

> 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.

Malcolm Kay