Linux: Recover Corrupted Partition From A Bad Superblock

by Vivek Gite · 12 comments

Q. How can I Recover a bad superblock from a corrupted ext3 partition to get back my data? I'm getting following error:

/dev/sda2: Input/output error
mount: /dev/sda2: can't read superblock

How do I fix this error?

A. Linux ext2/3 filesystem stores superblock at different backup location so it is possible to get back data from corrupted partition.

WARNING! Make sure file system is UNMOUNTED.

If your system will give you a terminal type the following command, else boot Linux system from rescue disk (boot from 1st CD/DVD. At boot: prompt type command linux rescue).

Mount partition using alternate superblock

Find out superblock location for /dev/sda2:
# dumpe2fs /dev/sda2 | grep superblock
Sample output:

  Primary superblock at 0, Group descriptors at 1-6
  Backup superblock at 32768, Group descriptors at 32769-32774
  Backup superblock at 98304, Group descriptors at 98305-98310
  Backup superblock at 163840, Group descriptors at 163841-163846
  Backup superblock at 229376, Group descriptors at 229377-229382
  Backup superblock at 294912, Group descriptors at 294913-294918
  Backup superblock at 819200, Group descriptors at 819201-819206
  Backup superblock at 884736, Group descriptors at 884737-884742
  Backup superblock at 1605632, Group descriptors at 1605633-1605638
  Backup superblock at 2654208, Group descriptors at 2654209-2654214
  Backup superblock at 4096000, Group descriptors at 4096001-4096006
  Backup superblock at 7962624, Group descriptors at 7962625-7962630
  Backup superblock at 11239424, Group descriptors at 11239425-11239430
  Backup superblock at 20480000, Group descriptors at 20480001-20480006
  Backup superblock at 23887872, Group descriptors at 23887873-23887878

Now check and repair a Linux file system using alternate superblock # 32768:
# fsck -b 32768 /dev/sda2
Sample output:

fsck 1.40.2 (12-Jul-2007)
e2fsck 1.40.2 (12-Jul-2007)
/dev/sda2 was not cleanly unmounted, check forced.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
Free blocks count wrong for group #241 (32254, counted=32253).
Fix? yes

Free blocks count wrong for group #362 (32254, counted=32248).
Fix? yes

Free blocks count wrong for group #368 (32254, counted=27774).
Fix? yes
..........
/dev/sda2: ***** FILE SYSTEM WAS MODIFIED *****
/dev/sda2: 59586/30539776 files (0.6% non-contiguous), 3604682/61059048 blocks

Now try to mount file system using mount command:
# mount /dev/sda2 /mnt
You can also use superblock stored at 32768 to mount partition, enter:
# mount sb={alternative-superblock} /dev/device /mnt
# mount sb=32768 /dev/sda2 /mnt

Try to browse and access file system:
# cd /mnt
# mkdir test
# ls -l
# cp file /path/to/safe/location

You should always keep backup of all important data including configuration files.

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{ 12 comments… read them below or add one }

1 Gypsy Chief 04.15.09 at 12:18 am

Well written article with lots of good information.
Does any of this work on OpenBSD and the ffs
file system?

2 yakub pashas 06.24.09 at 2:08 pm

thank you very much for the valuable inforamation

3 tuxsun1 08.03.09 at 10:49 pm

Lately I’ve noticed that when I Google on Linux questions, this site consistently returns the best or one of the best responses to what I was trying to solve. Because of that, I have signed up for your daily newsletter. Thanks for the great site!!

4 George 08.21.09 at 6:00 am

Very good information.

5 Martin 09.02.09 at 9:26 pm

Awesome. Thanks.
This is exactly what I needed instead of all the opinion with no solution.

6 Phillip 10.07.09 at 5:06 pm

Awesome. Worked Perfectly on RHEL5

7 Phillip 10.07.09 at 5:10 pm

Worked perfectly under RHEL5. Notes on my issue are below

I was getting following error when mounting.
Wrong fs type, bad option, bad superblock on /dev/sdd1
missing codepage or other error
In some cases usefull info is foinf in syslog – try
dmesg | tail or so

dmeg | tail displayed
EXT3-fs: filesystem has both journal and inode journals!

I tried useing the tune2fs -f -O ^has_journal /dev/sdd1 to remove the journal and try recreating but it did not work. tune2fs just hung there sucking 100% CPU when trying to remove the journal

The command given here worked great.

8 rick 10.29.09 at 6:42 pm

Does not seem to work, when I run dumpefs all it says:

“Bad magic number in super-block while trying to open…”

I already know the superblock is bad.

9 ShadowCat8 11.02.09 at 11:33 pm

Another way to cut to the quick of finding out where your superblocks should be after losing your primary is to use the following command:
# mke2fs -n /dev/[device and partition number]
This is making the utility you used to create the filesystem tell you where the backups are. You get a response similar to this:
# mke2fs -n /dev/sdb1
mke2fs 1.39 (29-May-2006)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
62248 inodes, 248976 blocks
12448 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
31 block groups
8192 blocks per group, 8192 fragments per group
2008 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729, 204801, 221185

Now, remember when using this command, you need to use the same flags you used when you created the filesystem originally, and just add ‘-n’ to them. If you made an ext3 filesystem, you would use:
# mke2fs -j -n /dev/[device and partition number]

HTH.

10 uncle max 12.28.09 at 7:06 am

Hi, this looks like a potential lifesaver. Great Stuff. Question: do superblocks ever move?? Obviously i don’t know ext3 filesystem internals — too much to learn, so little time… My point is: would there be any value in storing the list of superblock locations offline?

Thanks,
Marty.

11 Vivek Gite 12.28.09 at 11:33 am

@uncle max

You can.. but I strongly recommend backup instead of just superblocks. Linux comes with rsnapshot backup tool that can make hourly, daily and weekly backup of all your servers. If you are old school UNIX person, tar, dump and restore are regular tools for backup.

HTH

12 Evan 01.03.10 at 2:39 am

thank you so much, this is valuable information, and it saved me a LOT of work!!!!!

thanks for the write up, awesome, worked like a charm on ubuntu 9.10 off live cd rescuing a / partition on my HDD

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