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 }
Well written article with lots of good information.
Does any of this work on OpenBSD and the ffs
file system?
thank you very much for the valuable inforamation
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!!
Very good information.
Awesome. Thanks.
This is exactly what I needed instead of all the opinion with no solution.
Awesome. Worked Perfectly on RHEL5
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.
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.
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/sdb1mke2fs 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.
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.
@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
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