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

Sergey 'DoubleF' Zaharchenko doublef at tele-kom.ru
Tue Jan 6 21:24:13 PST 2004

On Tue, 6 Jan 2004 11:39:57 -0800 (PST)
"Scott I. Remick" <scott at sremick.net> probably 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
> 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?

I mean trying to mount it, to fsck it, using dd|hd to find the
superblock, etc. I just want to be *really* sure we know what
we are doing.

While we are on that, do you have an empty disk to copy this disk's
contents to? I'm not sure, but maybe I have an idea...

> 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.


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