5

I understand that I can list the location of a filesystem's superblocks using the following commands.

Example

First get the device handle for the current directory.

$ df -h .
Filesystem                         Size  Used Avail Use% Mounted on
/dev/mapper/fedora_greeneggs-home  402G  146G  236G  39% /home

Then use this command to list the superblocks for handle /dev/mapper/fedora_greeneggs-home.

$ sudo dumpe2fs /dev/mapper/fedora_greeneggs-home | grep -i superblock
dumpe2fs 1.42.7 (21-Jan-2013)
  Primary superblock at 0, Group descriptors at 1-26
  Backup superblock at 32768, Group descriptors at 32769-32794
  Backup superblock at 98304, Group descriptors at 98305-98330
  Backup superblock at 163840, Group descriptors at 163841-163866
  Backup superblock at 229376, Group descriptors at 229377-229402
  Backup superblock at 294912, Group descriptors at 294913-294938
  Backup superblock at 819200, Group descriptors at 819201-819226
  Backup superblock at 884736, Group descriptors at 884737-884762
  Backup superblock at 1605632, Group descriptors at 1605633-1605658
  Backup superblock at 2654208, Group descriptors at 2654209-2654234
  Backup superblock at 4096000, Group descriptors at 4096001-4096026
  Backup superblock at 7962624, Group descriptors at 7962625-7962650
  Backup superblock at 11239424, Group descriptors at 11239425-11239450
  Backup superblock at 20480000, Group descriptors at 20480001-20480026
  Backup superblock at 23887872, Group descriptors at 23887873-23887898
  Backup superblock at 71663616, Group descriptors at 71663617-71663642
  Backup superblock at 78675968, Group descriptors at 78675969-78675994
  Backup superblock at 102400000, Group descriptors at 102400001-102400026

But how does one actually examine the contents of one of these superblocks?

5

I'm not sure how you can examine any particular superblock, but you can use this command to examine the general contents that all the superblocks share like so, using dumpe2fs.

$ sudo dumpe2fs /dev/mapper/fedora_greeneggs-home | less

Example

$ sudo dumpe2fs /dev/mapper/fedora_greeneggs-home | less
Filesystem volume name:   <none>
Last mounted on:          /home
Filesystem UUID:          xxxxxxx-xxxx-xxxx-xxxx-88c06ecdd872
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize
Filesystem flags:         signed_directory_hash 
Default mount options:    user_xattr acl
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              26722304
Block count:              106857472
Reserved block count:     5342873
Free blocks:              67134450
Free inodes:              25815736
First block:              0
Block size:               4096
Fragment size:            4096
Reserved GDT blocks:      998
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         8192
Inode blocks per group:   512
Flex block group size:    16
Filesystem created:       Sat Dec  7 20:41:58 2013
Last mount time:          Sun Dec 22 21:31:01 2013
...

References

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