[Techtalk] Bad Superblocks

[Conor Daly]

Sent this on Sunday last.  Somehow it didn't make it...

Conor
----- Forwarded message from Conor Daly <cdaly at Hobbiton.cod.ie> -----

Date: Sun, 1 Dec 2002 11:38:10 +0000
From: Conor Daly <cdaly at Hobbiton.cod.ie>
To: techtalk at linuxchix.com
Subject: Re: [Techtalk] Bad Superblocks

On Sat, Nov 30, 2002 at 02:13:06PM -0600 or so it is rumoured hereabouts, 
Judith Elaine Bush thought:
> On Sat, Nov 30, 2002 at 01:36:37PM +0000, Conor Daly wrote:
> >  
> > Can you loop mount the _files_?  Though, if you're having trouble mounting
> > the partitions, it's not very likely you'll be able to mount the files
> > either.
> > 
> > > is corrupt, and you might try running e2fsck with an alternate superblock:
> > >     e2fsck -b 8193 
> >       ^^^^^^^^^^^^^^
> 
> Same error. Are there other positions i might try for a superblock?
> 
> I followed the example in the  losetup man page; it didn't seem successful.
> 
> Thanks for the pointers,
> 
> judith
> 
>  
> 
> =====================================================
> # losetup  /dev/loop0 /User/blondie/TIA3/roar
> [root at TIA4:/]
> # mkfs -t ext2 /dev/loop0 100
> mke2fs 1.27 (8-Mar-2002)
> Filesystem label=
> OS type: Linux
> Block size=1024 (log=0)
> Fragment size=1024 (log=0)
> 16 inodes, 100 blocks
> 5 blocks (5.00%) reserved for the super user
> First data block=1
> 1 block group
> 8192 blocks per group, 8192 fragments per group
> 16 inodes per group
> 
> Writing inode tables: done
> Writing superblocks and filesystem accounting information: done
> 
> This filesystem will be automatically checked every 29 mounts or
> 180 days, whichever comes first.  Use tune2fs -c or -i to override.
 
> # ls -l /TIA3-B/part2/
> total 0
> 
> # mount -t ext2 /dev/loop0 /TIA3-B/part2/
> 
> # df
> Filesystem           1k-blocks      Used Available Use% Mounted on
> /dev/hda1              3937220    469992   3267224  13% /
> /dev/hda3              3937252   1723768   2013476  47% /usr
> /dev/hda5             19686804   5917716  12769044  32% /User/cowboy
> /dev/hda6             19686804   5860452  12826308  32% /User/blondie
> /dev/hda7             10879208    677988   9648588   7% /User/share
> /dev/hdd1              1999776   1120960    878816  57% /TIA3-D/part1
> /dev/hdd5              2028098   1370864    552412  72% /TIA3-D/part5
> /dev/hdd6              2028129    984918    938387  52% /TIA3-D/part6
> /dev/loop0                  93        13        75  15% /TIA3-B/part2
> 
> # ls -l /TIA3-B/part2/
> total 12
> drwx------    2 root     root        12288 Nov 30 11:56 lost+found/
> # ls -l /TIA3-B/part2/lost+found/
> total 0

ARRGGHHH!  NOO!

I didn't mean that!  I guess I should have detailed it...  

What you've done here has wiped the image file by putting a new filesystem
on it.  That is correct for the situation where you want to make a _new_
filesystem in a file.  Here, however, you already _have_ such an "fs in
file" so you simply want to loop mount _that_.  That's just a one-liner:

mount -o loop -t ext2 /User/blondie/TIA3/roar /TIA3-B/part2

should do it.  Unfortunately, your image file is now wiped but you _can_
get it back:

dd if=/dev/hdc2 of=/User/blondie/TIA3/roar

was that what you used to create the image file in the first place?  I'm
not that confident that you'll be able to loop mount the file if you
weren't able to mount the original partition but it's worth a try.  

Sorry I didn't detail the command earlier but I've been using 
"mount -o loop" for years now and I'd just assumed people would know...

Conor
-- 
Conor Daly <conor.daly at oceanfree.net>

Domestic Sysadmin :-)
---------------------
Faenor.cod.ie
 11:14am  up 25 days, 19:58,  0 users,  load average: 0.00, 0.00, 0.00
Hobbiton.cod.ie
 11:12am  up 25 days, 19:49,  2 users,  load average: 0.01, 0.02, 0.00

----- End forwarded message -----

-- 
Conor Daly <conor.daly at oceanfree.net>

Domestic Sysadmin :-)
---------------------
Faenor.cod.ie
 10:46am  up 27 days, 19:31,  0 users,  load average: 0.16, 0.06, 0.05
Hobbiton.cod.ie
 10:44am  up 27 days, 19:22,  2 users,  load average: 0.04, 0.10, 0.08