Incorrect super block on a disk

Joshua Oreman oremanj at
Mon May 5 16:11:46 PDT 2003

On Mon, May 05, 2003 at 02:04:35PM -0700 or thereabouts, Paul English seemed to write:
> On Sun, 4 May 2003, Greg 'groggy' Lehey wrote:
> > > it tries for an alternate superblock, fails and then I try doing
> > > fsck -b 32 (as recommended in the manpages) and I get the same error.
> > >
> > > Is there anything I'm doing wrong or something else to try?
> >
> > It seems pretty certain that whatever they sent back from the data
> > recovery house is not a UFS file system.  You should try to find out
> > how they got the data there.  I can't imagine them creating a new file
> > system.  Until you know that, there's not much point trying
> > alternatives, though some of them exist.
> I will check with them - it looks like they don't have someone I can talk
> to on Saturday. I believe though that they just did a bit-for-bit or
> byte-for-byte copy. The partition table information is still there - the
> output of disklabel shows what appears to me to be a valid disk label for
> all of the partitions, this one included.

file -s is your friend. Try:
# file -s /dev/da0s1
where da0s1 is the partition on the recovered disk. It should tell you
what type FS it is.

This is an extremely useful feature that very few people actually know

> > > Can I somehow regenerate the super block?
> >
> > Regenerating super blocks is simple: that's what newfs(8) does.  The
> > trick is keeping your data.
> Aah...
> Fortunately they still have the source data, and I can also do a dd of the
> partition to another drive before I go mucking with newfs.
> I don't suppose that newfs has a special option to just try to regenerate
> superblocks and save the data? In my web searching for solutions, it looks
> like Linux has a -S option for mke2fs that will attempt to rebuild
> superblocks while saving the data.
> Are there any other alternate superblocks? Again it appears that Linux
> saves them every 8K clusters, but the fsck manpage on freebsd only
> mentions that block 32 is usually an alternate.
> Paul
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-- Josh

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