Comment 0 for bug 518582

Symptoms: (Ubuntu 9.10 on an ext4 partition /dev/sda1)

1. Booting fails.

2. "mount /dev/sda1" /mnt gives "mount: you must specify the filesystem type"
    but "mount -t ext4 /dev/sda1" is successful

3. blkid /dev/sda1 returns nothing

4. blkid -p /dev/sda1 gives "ambivalent result (probably more filesystems on the device)"

 After installing util-linux-ng-2.17 from source:

5. wipefs /dev/sda1 returns:

    offset type
----------------------------------------------------------------
0x410 minix [filesystem]

0x438 ext4 [filesystem]
                     UUID: d3bb8e26-9798-49ce-bc57-afb6ca62a7ba

I was able to cure the problem by creating a file on "/dev/sda1" and whereby changing the number of free inodes. See http://ubuntuforums.org/showthread.php?t=1397193

My diagnosis:

Minix uses the "magic number" 6824 at the location 0x410 to mark a Minix file system.

0x410 is also the location any ext filesystem uses to record the number of free inodes.
(The number of free inodes is essentially the number of files you are still able to create on the file system)

9320 in little endian decoding is "6824"

If the number of free inodes happens to be 9320 plus a multiple of 65536, then the ext filesystem will write 6824 to the 0x410 location.

So many programs will gets confused and don't know whether the files system is Minix or Ext.