Bad magic number in super-block

Bad magic number in super-block

Post by Hank Aria » Wed, 10 May 1995 04:00:00

now, i'm getting this error:
        bash# /sbin/e2fsck -b 8193 /dev/hdb1
        NEW e2fsck 0.0, 09-Feb94 for EXT2 FS 0.5, 94/03/10
        Block bitmap 0 for group 0 not in group
is there any remedy at this point?


: I have recently run into a problem that I cannot solve.  My filesystem crashed
: while I was updating to kernel 1.2.8.  Now, e2fsck says that there is a Bad
: magic number in super-block while trying to open /dev/hdb1.  tune2fs returns
: the same error.  Will mke2fs and mksuper overwrite the existing filesystem
: completely, or is there something else I can do to make e2fsck recognize the
: filesystem.

: I'd appreciate any email responses.


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


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

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