Baslinux mailing list

[sindi keesan <keesan AT sdf.lonestar.org>]

On Sun, 27 Feb 2005, Alejandro Lieber wrote:

> After using BL3 for several months, I get the following error trying
> to boot form the HD:
>
>
> EXT2-fs error ...ext2_check_descriptor: Block bitmap for group 0 not
> in group !
> EXT2-fs: group descriptor corrupted |
>
> Any ideas.
>
> Thank a lot.

I did a websearch on 'Block bitmap for group 0' and found that someone 
else fixed the problem with e2fsck -b (location of superblock backup) 
which is how I once fixed a problem of my own (which turned out, I think, 
to be due to the hard drive going bad).

My Linux Doctor suggests that you try e2fsck -b 8193 (partition) and says 
the copies are stored at selected locations on boundaries which are 8 
blocks apart.  Note that they have a number which is divisible by 8 with 1 
left over.  You can try this number, or subtract 1, multiply it by various 
other numbers and add 1 again.  If you read below the author used an even 
number but I think I had to use an odd number.  Read in the man page for 
e2fsck which also suggests numbers (the first one suggested there worked 
for me).

Boot with 2-floppy BL3 or loop BL3 to check the hard drive version, which 
has to be unmounted when using e2fsck.



             [ILUG-BOM] Resolved: unusual filesystem crash (long)

   erle [4]linuxers AT mm.ilug-bom.org.in
   Thu Dec 13 00:22:06 2001

I know i started this thread... but i got my answers,  and I guess it may
help someone .....

this is a really strange error. I  finally got down to the bottom of this
> From all the searching i got this in brief.
for those who want more details... do a search from google/linux  for
"ext2_check_descriptors group descriptors corrupted"
-
the problem seems to have surfaced sometime after the release of the 2.2
series kernel . Not specific to any distro . Various explainations...
basically random error usually related to new / development drivers (
motherboard chipset, udma...)

....
> 2. Does fsck pass? Even if you force a check with -f?
no it fails... doesn't even start actually .. its no good.

> 3. What about badblocks?
    doesn't do much..

it can't
reason being. this : "Block Bitmap for group 0 not in group" & "group
descriptors corrupted" errors.
-
the filesystem reports as being unformatted ( cannot mount "/")  ( from
rescue disk)

now when you format a disk.. as usual superblock backups are stored at
veriuos locations inside the Hdd. mke2fs usually spits out a series of
numbers related to where it has stored these backups.. _ SAVE THIS _
 most ignore.

i recovered my data in this fashion  (e2fsck promts for this) " e2fsck -b
327680 /dev/hda5"
where the number is the stored location & -b forces it to look@ this block.
( then run fsck... a few till you get it clean !)

my filestystem was stored with 4096 block size. that number (327680 )  is
basically a multiple of 80.

[But since the first blocks is 1, you will probably  have to add 1 to this 
multiple - Sindi]

so you will have to try starting from block 1 ( useless now b/c if it was
working .. u wouldn't be trying this.) in multiples of your filesystem. from
what I gather its not stored at each multiple... but at a few of them.
long & tediuos perhaps.. but serves you . .... me ? :-)  right for not
storing those superblock backups.
( for those of you giggling away... no I did not do this 80 times... )

if that doesn't work... my guess is...  Format
:-)

C'ya
Erle.