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Maxabout.com > Tips
Damaged SuperblockAdded on:9/3/2008 10:58:11 PM
In Linux Tips Rated by 1 users
- If a filesystem check fails and returns the error message “Damaged Superblock” you're lost . . . . . . . or not ?
- Well, not really, the damaged ¨superblock¨ can be restored from a backup. There are several backups stored on the harddisk. But let me first have a go at explaining what a “superblock”is.
- A superblock is located at position 0 of every partition, contains vital information about the filesystem and is needed at a fielsystem check.
- The information stored in the superblock are about what sort of fiesystem is used, the I-Node counts, block counts, free blocks and I-Nodes, the numer of times the filesystem was mounted, date of the last filesystem check and the first I-Node where / is located.
- Thus, a damaged superblock means that the filesystem check will fail.
- Our luck is that there are backups of the superblock located on several positions and we can restore them with a simple command.
- The usual ( and only ) positions are: 8193, 32768, 98304, 163840, 229376 and 294912. ( 8193 in many cases only on older systems, 32768 is the most current position for the first backup )
- You can check this out and have a lot more info about a particular partition you have on your HD by:
CODE
$ dumpe2fs /dev/hda5
- You will see that the primary superblock is located at position 0, and the first backup on position 32768.
- O.K. let´s get serious now, suppose you get a ¨Damaged Superblock¨ error message at filesystem check ( after a power failure ) and you get a root-prompt in a recovery console, then you give the command:
CODE
# e2fsck -b 32768 /dev/hda5
( don´t try this at home . . uh, I mean: don´t try this on a mounted filesystem )
- It will then check the filesystem with the information stored in that backup superblock and if the check was successful it will restore the backup to position 0.
- Now imagine the backup at position 32768 was damaged too . . . then you just try again with the backup stored at position 98304, and 163840, and 229376 etc. etc. until you find an undamaged backup ( there are five backups so if at least one of those five is okay it´s bingo ! )
- So next time don´t panic . . just get the paper where you printed out this Tip and give the magic command
CODE
# e2fsck -b 32768 /dev/hda5
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