voa

Hi,

I have used installed a centos 4 distribution in my PC for a few months which was quite good. However, the system failed to start last week and shown the following message on startup:
//----------------------------------------------------------------------------------
booting 'CentOS (2.6.9-5.0.5.EL)'
root (hd0, 0)

filesystem type is ext2fs, patition type 0x83
kernel /vmlinuz=2.6.9-5.0.5.EL ro root=/dev/VolGroup00/LogVol00 rhgb quiet
[Linux-bzImage, setup=0x1400, size=0x15cbd4]
initrd /initrd-2.6.9-5.0.5.EL. img
[Linux-initrd @ 0xfdfb000, 0xeee2bd bytes]

Uncompressing Linux.... ok, booting the kernel.
audit(1119364802.006:0): initialized
Red Hat nash version 4.1.18 starting
File descriptor 3 left open
reading all physical volumes. This may take a while....
/dev/hdc: open failed: No medium found
/dev/hdd: open failed: No medium found
Found volume group "VolGroup00" using metadata type lvm2
File descriptor 3 left open
2 logical volume(s) in volume group "VolGroup00" now active
File descriptor 3 left open
EXT3-fs: unable to read superblock
mount: error 22 mounting ext3
mount: error 2 mounting none
switchroot: mount failed: 22
umount /initrd/dev failed: 2
Kernel panic - not syncing: Attempted to kill init!
//----------------------------------------------------------------------------------

I have tried to

1) linux rescue
2) skip mounting and go to command prompt
3) enable lvm and tried fsck for the volumes (one is empty volume? and another failed)
4) run fdisk to list devices
5) fsck.ext3 the devices
6) run fsck again and specify the superblock number as suggested (from the prompt and "mke2fs -n /dev/hda2) but all failed for /dev/hda2

Fyi, I remember I have choosen to put everything (except /boot) under / during linux installation and the file system is ext3.

I guess /dev/hda1 is /boot and /dev/hda2 forms the volume group 'VolGroup00' with 'LogVol01' as used-block volume and 'LogVol00' as unused-block volume. It seems that the superblock got corrupted and the backup superblock number cannot be determined correctly. I am not sure whether I should deal with the logical volume or the device with fsck. Or I am heading towards a wrong direction. Please help. I really need the data.

The actual screen dump is as below.

Thanks,

VOA
---------------------------------------------------------------------------------------------------------------

#lvm lvscan
inactive '/dev/VolGroup00/LogVol00' [76.03GB] inherit
inactive '/dev/VolGroup00/LogVol01' [512.00 MB] inherit

#lvm vgchange -ay
2 logical volume(s) in volume group "VolGroup00" now active

#fsck -f /dev/VolGroup00/LogVol00
fsck 1.35 (28-Feb-2004)
WARNING: couldn't open /etc/fstab: No such file or directory
e2fsck 1.35 (28-Feb-2004)
fsck.ext2: Attempt to read block from filesystem resulted in short read while trying to open /dev/VolGroup00/LogVol00
Could this be a zero-length partition?

#fsck -f /dev/VolGroup00/LogVol01
fsck 1.35 (28-Feb-2004)
WARNING: couldn't open /etc/fstab: No such file or directory
fsck: fsck.swap: not found
fsck: Error 2 while executing fsck.swap for /dev/VolGroup00/LogVol01

#fdisk -l
device boot start end blocks id system
/dev/hda1 * 1 13 104391 83 linux
/dev/hda2 14 10011 80308935 8e linux LVM

#fsck.ext3 /dev/hda1
e2fsck 1.35 (28-Feb-2004)
/boot: clean, 38/26104 files, 15417/104388 blocks

#fsck.ext3 /dev/hda2
e2fsck 1.35 (28-Feb-2004)
couldn't find ext2 superblock, trying backup blocks....
fsck.ext3: bad magic number in super-block while trying to open /dev/hda2

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

#e2fsck -b 8193 /dev/hda2
e2fsck 1.35 (28-Feb-2004)
e2fsck: bad magic number in super-block while trying to open /dev/hda2

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

#mke2fs -n /dev/hda2
mke2fs 1.35 (28-Feb-2004)
max_blocks 4294967295, rsv_groups = 0, rsv_gdb = 1024
Filesystem label =
OS type: linux
block size=4096 (log=2)
fragment size=4096 (log=2)
10043392 inodes, 20077234 blocks
1003861 blocks (5.00 %) reserved for the super user
first data block=0
maximum filesystem blocks=20971520
613 block groups
32768 blocks per group, 32768 fragments per grup
16384 inodes per group
superblock backs stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424

#e2fsck - b 32768 /dev/hda2
e2fsck 1.35 (28-Feb-2004)
e2fsck: bad magic number in super-block while trying to open /dev/hda2

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

#e2fsck -b (98304, 163840 ....) /dev/hda2

(i tried 4 of them which were all failed, I wonder if the backup superblock (or block size) is applicable here or I should target at the logical volume instead of device using some other command to fix the superblock?????)

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anomie

How are you determining the appropriate backup superblock? Did you make notes of it when you created the filesystem?

There is a howto here on finding a backup superblock: http://forums.suselinuxsupport.de/in...howtopic=14152

Note that this was written for SuSE, but the ext2/3 utilities should work the same in your case (I think).

One thing I would add to the howto is that you may also be able to use on the unmounted device to find the backup superblock. That would probably be easier in your case.

voa

Hi anomie,

I used "mke2fs -n /dev/hda2" to determine the backup superblocks and I have tried all of them with no avail.

I have tried e2fsck for the LV but shown the following messages.

Also, I have also tried to mount the data regardless of error, but failed.

I just wonder what I can do to recover the data?

Thanks,

VOA

--------------------------------------------------------------
#e2fsck /dev/VolGroup00/LogVol00
e2fsck 1.35 (28-Feb-2004)
e2fsck: Attempt to read block from filesystem resulted in short read while trying to open /dev/VolGroup00/LogVol00
Could this be a zero-length partition?


#e2fsck /dev/VolGrup00/LogVol01
e2fsck 1.35 (28-Feb-2004)
couldn't find ext2 superblock, trying backup blocks....
e2fsck: bad magic number in super-block while trying to open /dev/VolGroup00/LogVol01

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

#lvm pvscan
PV /dev/hda2 VG VolGroup00 lvm2 [76.56 GB / 32.00 MB free]
Total: 1 [76.56 GB] / in use: 1 [76.56 GB] / in no VG: 0 [0 ]

#lvm lvscan
active '/dev/VolGroup00/LogVol00' [76.03GB] inherit
active '/dev/VolGroup00/LogVol01' [512.00 MB] inherit

#fdisk -l
device boot start end blocks id system
/dev/hda1 * 1 13 104391 83 linux
/dev/hda2 14 10011 80308935 8e linux LVM

#mount -o errors=continue /dev/hda2 /sysimage
mount: Mounting /dev/hda2 on /sysimage failed: device or resource busy

#mount -o errors=remount-ro /dev/hda2 /sysimage
mount: Mounting /dev/hda2 on /sysimage failed: device or resource busy

#mount -o errors=continue /dev/VolGroup00/LogVol00 /sysimage
mount: mounting /dev/VolGroup00/LogVol00 on /sysimage failed: invalid arguement

#mount -o errors=continue /dev/VolGroup00/LogVol01 /sysimage
mount: mounting /dev/VolGroup00/LogVol01 on /sysimage failed: invalid arguement

#mount /dev/VolGroup00/LogVol01
mount: cannot read /etc/fstab: no such file or directory

Salient

The very first piece of info read from a disk is it's Superblock ... which includes the disk's geometry information, available free space, and most important is the location of the first i-node.

Since ext2 and ext3 file systems place numerous copy's of the Superblock throughout the disk -one Superblock after every Group block- a group block is equal to 8192 blocks ... thus, the first redundant Superblock would be at 8193, second at 16385 - etc ...
Try this parameter with the mount -o command on an Ext2 filesystem "sb=n" (without quotes) this tells mount to use block n as the Superblock.

Example: mount -o sb=n /dev/hda1 /usr

Indigno

well, worst come to worst, plug your hard drive into another computer, grab your files you want saved, and wipe your drive. always have a backup plan

loft306

voa: what did you do just b4 you rebooted? did you change anything? like a kernel or /etc/fstab ?

__________________
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Testing? What's that? If it compiles, it is good, if it boots up, it is perfect. ~ Linus Torvalds
http://loft306.org

antonmx

I had the same problem and tried everything from this topic. In my case I have successfully run "e2fsck -b=32768 /dev/..." and the same with "-y", "-p", "-c", "-cc" options. At the end it always outputed the correct information on numbers of files and folders, usage statistics and so on. However it did not help me - the error continued. So I was almost to reformat the drive (I could not make dd since it was 300Gb disk and I had none of the same size).

BUT! Before that I connected the harddisk to a PC with winXP installed. And tried to check it with the "Ext2+Reiser" plugin of Total Commander. Can you belive that, it worked! As if there were no problems at all. I have rescued ALL the data on that broken disk!

Tell you what? I am a fan of Linux for longer than 3 years, but time to time smth. happens what makes me keep win as the secondary OS...((( What a pity!!!

Hope this can help someone.

damber

Just in case anyone else finds this thread with RAID/LVM superblock issues... I found this article particularly useful: http://www.linuxjournal.com/article/8874

coljac

I came to this thread via Google. Yep, I had all the same problems and tried everything to get my LVM to mount after it stopped booting due to a "Machine Check Exception". The only thing that worked after all those hours was explore2fs on Windows XP, which worked like a charm - I recovered the data I needed. Quite surprising than Windows came to the rescue.

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