dumpe2fs and fsck -b for ext2/ext3 file system

If the default superblock of a ext2/ext3 file sytem is damaged. You may use dumpe2fs to view the location of backup superblock and then use fsck -b to repair the file sytem.

An example of dumpe2fs output: red is the backup superblock

+++++++++++++++++++++++++++++++++++++++++++++
c1:~ # dumpe2fs /dev/sda1
dumpe2fs 1.41.1 (01-Sep-2008)
Filesystem volume name:
Last mounted on:
Filesystem UUID: 2963e327-deeb-4265-a1e1-1a4e5c0f34dd
Filesystem magic number: 0xEF53
Filesystem revision #: 1 (dynamic)
Filesystem features: has_journal ext_attr resize_inode dir_index filetype needs_recovery sparse_super
Filesystem flags: signed_directory_hash
Default mount options: (none)
Filesystem state: clean
Errors behavior: Continue
Filesystem OS type: Linux
Inode count: 18072
Block count: 72260
Reserved block count: 3613
Free blocks: 50006
Free inodes: 18028
First block: 1
Block size: 1024
Fragment size: 1024
Reserved GDT blocks: 256
Blocks per group: 8192
Fragments per group: 8192
Inodes per group: 2008
Inode blocks per group: 251
Filesystem created: Mon Aug 31 23:12:55 2009
Last mount time: Sun Oct 4 16:39:06 2009
Last write time: Sun Oct 4 16:39:06 2009
Mount count: 30
Maximum mount count: -1
Last checked: Mon Aug 31 23:12:55 2009
Check interval: 0 ()
Reserved blocks uid: 0 (user root)
Reserved blocks gid: 0 (group root)
First inode: 11
Inode size: 128
Journal inode: 8
Default directory hash: half_md4
Directory Hash Seed: 08edb5d9-25d8-4092-8a2a-36de718d1aaa
Journal backup: inode blocks
Journal size: 4113k


Group 0: (Blocks 1-8192)
Primary superblock at 1, Group descriptors at 2-2
Reserved GDT blocks at 3-258
Block bitmap at 259 (+258), Inode bitmap at 260 (+259)
Inode table at 261-511 (+260)
3057 free blocks, 1982 free inodes, 2 directories
Free blocks: 526-2560, 2998-3584, 4869-5303
Free inodes: 27-2008
Group 1: (Blocks 8193-16384)
Backup superblock at 8193, Group descriptors at 8194-8194
Reserved GDT blocks at 8195-8450
Block bitmap at 8451 (+258), Inode bitmap at 8452 (+259)
Inode table at 8453-8703 (+260)
0 free blocks, 2008 free inodes, 0 directories
Free blocks:
Free inodes: 2009-4016
Group 2: (Blocks 16385-24576)
Block bitmap at 16385 (+0), Inode bitmap at 16386 (+1)
Inode table at 16387-16637 (+2)
5864 free blocks, 2008 free inodes, 0 directories
Free blocks: 16638-16640, 18716-24576
Free inodes: 4017-6024
Group 3: (Blocks 24577-32768)
Backup superblock at 24577, Group descriptors at 24578-24578
Reserved GDT blocks at 24579-24834
Block bitmap at 24835 (+258), Inode bitmap at 24836 (+259)
Inode table at 24837-25087 (+260)
7681 free blocks, 2008 free inodes, 0 directories
Free blocks: 25088-32768
Free inodes: 6025-8032
Group 4: (Blocks 32769-40960)
Block bitmap at 32769 (+0), Inode bitmap at 32770 (+1)
Inode table at 32771-33021 (+2)
3826 free blocks, 2008 free inodes, 0 directories
Free blocks: 37135-40960
Free inodes: 8033-10040
Group 5: (Blocks 40961-49152)
Backup superblock at 40961, Group descriptors at 40962-40962
Reserved GDT blocks at 40963-41218
Block bitmap at 41219 (+258), Inode bitmap at 41220 (+259)
Inode table at 41221-41471 (+260)
7681 free blocks, 2008 free inodes, 0 directories
Free blocks: 41472-49152
Free inodes: 10041-12048
Group 6: (Blocks 49153-57344)
Block bitmap at 49153 (+0), Inode bitmap at 49154 (+1)
Inode table at 49155-49405 (+2)
7746 free blocks, 1990 free inodes, 1 directories
Free blocks: 49407-51712, 51715-52736, 52924-53760, 53764-57344
Free inodes: 12067-14056
Group 7: (Blocks 57345-65536)
Backup superblock at 57345, Group descriptors at 57346-57346
Reserved GDT blocks at 57347-57602
Block bitmap at 57603 (+258), Inode bitmap at 57604 (+259)
Inode table at 57605-57855 (+260)
7681 free blocks, 2008 free inodes, 0 directories
Free blocks: 57856-65536
Free inodes: 14057-16064
Group 8: (Blocks 65537-72259)
Block bitmap at 65537 (+0), Inode bitmap at 65538 (+1)
Inode table at 65539-65789 (+2)
6470 free blocks, 2008 free inodes, 0 directories
Free blocks: 65790-72259
Free inodes: 16065-18072
c1:~ #
++++++++++++++++++++++++++++++++++++++++++++++++

then run:

e2fsck -f -b 8193 /dev/sda1