Recover original superblock on corrupted filesystem?
bloch at verdurin.com
bloch at verdurin.com
Tue Oct 25 22:05:21 UTC 2005
On Tue, 25 Oct 2005, Stephen C. Tweedie wrote:
> Hi,
>
> On Fri, 2005-10-21 at 15:51 +0100, bloch at verdurin.com wrote:
>
> > It appears the original superblock is corrupted too, as it has an inode
> > count of 0. When I start fsck with -b 32760, it uses the alternate
> > superblock and proceeds. However, it restarts from the beginning a
> > couple of times and after the second restart it doesn't use the
> > alternate superblock, stopping instead as it can't find the original
> > one.
>
> Do you have a log of the fsck output, and which e2fsprogs version is
> this? Sounds like it may be an e2fsck bug if we don't honour the backup
> superblock flag on subsequent passes.
>
I do have a log, yes. It's rather large...
It's version 1.38
> > Is there a way around this, such as using one of the alternate
> > superblocks to replace the broken one
>
> Yes, "dd" of the appropriate block should work... but do this with
> extreme care, as getting it slightly wrong will cause major havoc.
>
> "debugfs" may be a better bet.
>
> # debugfs -w -b$BLOCKSIZE -s$SUPERBLOCK /dev/$DEV
>
> will tell debugfs to read the specified superblock. If you dirty the
> superblock (eg. with the "dirty" command) then quit, it will write back
> the backup superblock to the home location too.
>
In the end I managed to get the filesystem to mount (after a six-hour
fsck), backed up the data and have since wiped that partition.
Thanks for the tip, though. I'll see if I can compress and/or edit the
log to a sensible size.
Adam
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