Comment 3 for bug 1011007

Same problem here: After a reboot, Ubuntu 12.04 didn't mount the rootfs properly anymore, dropping me into busybox with a misleading error message (cf. attached acreenshot). Looks like libblkid looks for the magic number 0x2F000000 at byte 96 of the last (partial) 512 byte block of the device. Unfortunatley whatever file was written there was full of this magic number:

root@Otherland:~# blkid -p /dev/mapper/hd-sys
/dev/mapper/hd-sys: VERSION="12032.0" TYPE="silicon_medley_raid_member" USAGE="raid"
root@Otherland:~# env BLKID_DEBUG=0xffff blkid -p /dev/mapper/hd-sys
libblkid: debug mask set to 0xffff.
allocate a new probe 0x1f22030
ready for low-probing, offset=0, size=14147387392
found entire diskname for devno 0xfc0a
whole-disk: YES, regfile: NO
zeroize wiper
chain safeprobe superblocks ENABLED
--> starting probing loop [SUBLKS idx=-1]
[0] linux_raid_member:
        call probefunc()
        buffer read: off=14147321856 len=64 pr=0x1f22030
        buffer read: off=14147379200 len=256 pr=0x1f22030
        buffer read: off=0 len=256 pr=0x1f22030
        buffer read: off=4096 len=256 pr=0x1f22030
[1] ddf_raid_member:
        call probefunc()
        buffer read: off=14147386880 len=512 pr=0x1f22030
        buffer read: off=14147255808 len=512 pr=0x1f22030
[2] isw_raid_member:
        call probefunc()
        buffer read: off=14147386368 len=48 pr=0x1f22030
[3] lsi_mega_raid_member:
        call probefunc()
        reuse buffer: off=14147386880 len=512 pr=0x1f22030
[4] via_raid_member:
        call probefunc()
        reuse buffer: off=14147386880 len=512 pr=0x1f22030
[5] silicon_medley_raid_member:
        call probefunc()
        reuse buffer: off=14147386880 len=512 pr=0x1f22030
assigning VERSION [superblocks]
assigning TYPE [superblocks]
assigning USAGE [superblocks]
<-- leaving probing loop (type=silicon_medley_raid_member) [SUBLKS idx=5]
chain safeprobe topology DISABLED
chain safeprobe partitions ENABLED
zeroize wiper
returning TYPE value
returning VERSION value
/dev/mapper/hd-sys: VERSION="12032.0" returning TYPE value
TYPE="silicon_medley_raid_member" returning USAGE value
USAGE="raid"
reseting probing buffers pr=0x1f22030
buffers summary: 1904 bytes by 7 read() call(s)
free probe 0x1f22030
root@Otherland:~# wipefs /dev/mapper/hd-sys
offset type
----------------------------------------------------------------
0x438 ext4 [filesystem]
                     LABEL: root
                     UUID: 55c1f04f-4e15-48e4-9f21-8f71657d0682

0x34b3ffe60 silicon_medley_raid_member [raid]

root@Otherland:~# blkid -h | grep util-linux
blkid from util-linux 2.20.1 (libblkid 2.20.0, 19-Oct-2011)
root@Otherland:~# dd if=/dev/mapper/hd-sys bs=1 skip=14147386880 count=512 | od -v -tx1z
512+0 records in
512+0 records out
0000000 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000020 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000040 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000060 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000100 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000120 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000140 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000160 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000200 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000220 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000240 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000260 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000300 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000320 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000340 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000360 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000400 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000420 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000440 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 2f >.../.../.../.../<
0000460 00 00 00 2f 00 00 00 2f 00 00 00 2f 00 00 00 30 >.../.../.../...0<
0000500 00 00 00 30 00 00 00 30 00 00 00 31 00 00 00 32 >...0...0...1...2<
0000520 00 00 00 34 00 00 00 35 00 00 00 37 00 00 00 3a >...4...5...7...:<
0000540 08 08 08 40 6c 6c 6c 74 ae ae ae d6 c0 c0 bf fe >...@lllt........<
0000560 c0 c0 c0 ff c6 c6 c5 ff cb cb ca ff cb cb ca ff >................<
0000600 ca ca c8 ff d0 d0 ce ff d0 d0 cf ff d1 d1 cf ff >................<
0000620 cf cf cd ff d0 d0 ce ff d9 d9 d7 ff d3 d3 d0 ff >................<
0000640 d3 d3 d1 ff cf cf cd ff d2 d2 d0 ff d5 d5 d2 ff >................<
0000660 d8 d9 d7 ff d9 da d6 ff c2 c3 c0 e7 07 07 07 8c >................<
0000700 00 00 00 85 00 00 00 81 00 00 00 7d 00 00 00 78 >...........}...x<
0000720 00 00 00 74 00 00 00 70 00 00 00 6a 00 00 00 66 >...t...p...j...f<
0000740 00 00 00 60 00 00 00 5c 00 00 00 58 00 00 00 53 >...`...\...X...S<
0000760 00 00 00 4f 00 00 00 4b 00 00 00 48 00 00 00 44 >...O...K...H...D<
0001000
512 bytes (512 B) copied, 0.317732 s, 1.6 kB/s