Bad magic number in super-block / Group descriptors look bad

Bad magic number in super-block / Group descriptors look bad

Post by Screanj » Wed, 19 Sep 2001 10:40:40


Ever found yourself in this situation ?
You've had a power-failure or just did something very bad with your
and now when trying to mount it fsck screams:

Group descriptors look bad... trung backup blocks....
/sbin/e2fsck: Bad magic number in super-block while trying to open

I've had this problem 2 times before now, and i've had a hell of a
time finding any docs related. I DID eventually find this:
(Note: text below is copy-pasted together from several articles, and
so not
 written by myself...)

----- begin of article pastes ----------------

From MANPAGES of mke2fs:

Write superblock and group descriptors only. This is useful if all of
the superblock and backup superblocks are corrupted,
 and a last-ditch recovery method is desired. It causes mke2fs to
reinitialize the superblock and group descriptors, while not
 touching the inode table and the block and inode bitmaps. The e2fsck
program should be run immediately after this option is used,
 and there is no guarantee that any data will be salvageable.

Ofcourse you're should only try this when you've exhausted all other
Other options are:

fsck -b 32 /dev/hdb1  (use the first backup super-block)

To determine the locations of the backup superblocks:
# newfs -N /dev/r

    Caution: Use the "N" option. If the "n" option is used, the
             may be destroyed.

Example using fsck on a backup superblock:

     /dev/rsd1a:   204540 sectors in 974 cylinders of 6 tracks, 35
     104.7MB in 61 cyl groups (16 c/g, 1.72MB/g, 768 i/g)
     super-block backups (for fsck -b #) at:
     32, 3440, 6848, 10256, 13664, 17072, 20480, 23888, 26912,
     30320, 33728, 37136, 40544, 43952, 47360, 50768, 53792, 57200,
     60608, 64016, 67424, 70832, 74240, 77648, 80672, 84080, 87488,
     90896, 94304, 97712, 101120, 104528, 107552, 110960, 114368,
     121184, 124592, 128000, 131408, 134432, 137840,141248, 144656,
     151472, 154880, 158288, 161312, 164720, 168128, 171536, 174944,
     181760, 185168, 188192, 191600, 195008, 198416, 201824,

         In this example, 201824 is the last backup superblock
         198416 is the next to last backup superblock location.

------------- end of article pastes --------------
Also it's interesting to note that it seems the larger the disk
the less backup super-block are stored.. I my case, on a 40 GB Maxtor:

32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632,
2654208, 4096000

where the only backups, (the newfs command mentioned above, was not
installed here, and i could not find it anywhere) i learned this only
after mk2fs told me after it had written the new super-block to my

Hope this helpes some people !

Best regards,

Jan Wilmans


1. Newbie: Bad magic number in super-block

I am new to linux.  Someone left our company and gave me their PC and now when
I boot, I get the following messages:

fsck.ext2: Bad magic number in super-block while trying to open /dev/hda1

The superblock could not read or does not describe a correct ext2 filesystem.
If the device is valid and it really contains ext2 filesystem (and not swap or
ufs or something else), then the superblock is corrupt, and you might try
running e2fsck with an alternate superblock:
     e2fsck -b 8193 <device>

[/sbin/fsck.ext2] fsck.ext2 -a /dev/hda5
fsck.ext2: Bad magic number in super-block while trying to open /dev/hda5

And repeat the above paragraph.

******** An error occurred during file system check.
******** Dropping you to a shell; the system will reboot
******** When you leave the shell.
Give root password for the maintenance
(or control-D for normal startup)

What's going on?

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