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

[Sergey 'DoubleF' Zaharchenko]

On Wed, 4 Feb 2004 08:26:47 -0800 (PST)
"Scott I. Remick" <scott at sremick.net> probably wrote:

> 
> --- Sergey 'DoubleF' Zaharchenko <doublef at tele-kom.ru> wrote:
> > Try using fsck -n (answer `no'), and recording what else comes up.
> 
> That won't work, because it answers no to the first question of looking for
> alternate superblocks, then aborts immediately. So I'm just going to
> manually say no to all questions after yes to the first:
> 
> bash-2.05b# fsck /dev/ad2s1e
> ** /dev/ad2s1e
> BAD SUPER BLOCK: MAGIC NUMBER WRONG
> 
> LOOK FOR ALTERNATE SUPERBLOCKS? [yn] y
> 
> USING ALTERNATE SUPERBLOCK AT 32
> ** Last Mounted on
> ** Phase 1 - Check Blocks and Sizes
> 416 BAD I=2
> 412 BAD I=3
> 424 BAD I=4
> 414 BAD I=4
> 417 BAD I=5
> INCORRECT BLOCK COUNT I=4257794 (8928 should be 9952)
> CORRECT? [yn] n
> 
> 17227776 DUP I=4257795
> 17227777 DUP I=4257795
> 17227778 DUP I=4257795
> 17227779 DUP I=4257795
> 17227780 DUP I=4257795
> 17227781 DUP I=4257795
> 17227782 DUP I=4257795
> 17227783 DUP I=4257795
> 17227784 DUP I=4257795
> 17227785 DUP I=4257795
> 17227786 DUP I=4257795
> EXCESSIVE DUP BLKS I=4257795
> CONTINUE? [yn] n

Here you should have answered `y' (it doesn't ask you to change
anything yet). Let's try that again, shall we?

> UPDATE STANDARD SUPERBLOCK? [yn] n
> 
> 
> ***** FILE SYSTEM MARKED DIRTY *****

Well, after all fsck doesn't seem mad (`erase everything and mark fs
clean'). But if you are really are paranoid, as you should be, you
should copy the whole contents of the harddrive, maybe to a remote
machine, by dd (over NFS, perhaps). Perhaps the `sparse' dd option
would help save a bit of space (by creating `holes' in the file where
there were NUL's on the harddrive).

> > If you know what fsdb(8) is, it might be helpful (still with the -r
> > (read-only) option, and the -d option as well). I don't, but I'm
> > learning it intensively at the moment:).
> 
> I don't, and the man page sufficiently put the fear of the almighty in me as
> far as it goes "Use this tool with extreme caution--you can damage an FFS
> file system beyond what fsck(8) can repair."  It's also a bit out of my
> league as far as understanding how to make use of it. 

It's not harmful in `-r'-mode, but I'm afraid it won't help because it
wouldn't even use an alternate superblock, as I've found out.

> > > so I'd still need to fix that manually somehow... correct?
> > 
> > Yes, by means of dd.
> 
> Hmm although that last fsck question "UPDATE STANDARD SUPERBLOCK? [yn]"
> seemed interesting.
> 

That's another option.

-- 
DoubleF
An elephant is a mouse with an operating system.
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