Unable to change UUID - Bad magic number in super-block

cowmoo32 · 08-01-2013, 02:12 PM

I used clonezilla to clone an entire drive. My end goal is to run updates on this drive, boot from it, and migrate the updates over to the "original" drive. To keep the computer from getting confused when I boot with two identical drives, I need to change the UUID but I'm running into trouble.

Code:

# uuid
dc0e45c0-fada-11e2-8e97-2fa4191f2c28
# tune2fs /dev/sda2 -U 'dc0e45c0-fada-11e2-8e97-2fa4191f2c28'
tune2fs 1.41.12 (17-May-2010)
tune2fs: Bad magic number in super-block while trying to open /dev/sda2
Couldn't find valid filesystem superblock.

This is an LVM member if that makes any difference.

Code:

# fdisk -l

Disk /dev/sda: 250.0 GB, 250000000000 bytes
255 heads, 63 sectors/track, 30394 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00097d75

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          64      512000   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              64       30395   243627008   8e  Linux LVM

Ser Olmy · 08-01-2013, 02:40 PM

You cannot use tune2fs (or any other file system tool) on an LVM Physical Volume, simply because the file system isn't written directly to that volume. The file system is written to a Logical Volume, which exists inside a Volume Group, which consists of on one or more Physical Volumes.

Find the true identity of the device (the Logical Volume) the file system is on, and run tune2fs on that device instead.

michaelk · 08-01-2013, 02:40 PM

It does, an LVM partition is a container for logical volumes which are the actual filesystems. What linux distribution/version are you running?

You can change the UUIDs with the pvchange command but you also need to change the volume group name in order to mount the clone on the same system. You will need to boot from a rescue disk in order to rename your / logical volume.

cowmoo32 · 08-02-2013, 09:18 AM

Quote:

Originally Posted by Ser Olmy

You cannot use tune2fs (or any other file system tool) on an LVM Physical Volume, simply because the file system isn't written directly to that volume. The file system is written to a Logical Volume, which exists inside a Volume Group, which consists of on one or more Physical Volumes.

Find the true identity of the device (the Logical Volume) the file system is on, and run tune2fs on that device instead.

/dev/sda1 is my boot partition and /dev/sda2 is the LVM. Are you saying the 'true' UUID is on sda1?

Quote:

Originally Posted by michaelk

It does, an LVM partition is a container for logical volumes which are the actual filesystems. What linux distribution/version are you running?

You can change the UUIDs with the pvchange command but you also need to change the volume group name in order to mount the clone on the same system. You will need to boot from a rescue disk in order to rename your / logical volume.

I'm on RHEL 6. I was afraid of needing a rescue disk to change the volume group name and was hoping there was a way of avoiding that, oh well.

cowmoo32 · 08-02-2013, 09:48 AM

...

Code:

# blkid
/dev/mapper/vg_hallen4brxrc1-lv_root: UUID="d8e96ad4-45e8-44ce-b11d-acb71abf90c6" TYPE="ext4" 
/dev/sda2: UUID="7CBVuf-OmlK-2OnU-UVM0-O7nA-s8I3-zvOFKg" TYPE="LVM2_member" 
/dev/sda1: UUID="899895d5-6fb4-4c87-a761-65345e88174d" TYPE="ext4" 
/dev/mapper/vg_hallen4brxrc1-lv_swap: UUID="7450754c-e2a2-4516-b989-bfbb5e985de7" TYPE="swap" 
/dev/mapper/vg_hallen4brxrc1-lv_home: UUID="7aa466a7-ed56-4697-a228-086b2749f390" TYPE="ext4" 
# blkid
/dev/mapper/vg_hallen4brxrc1-lv_root: UUID="d8e96ad4-45e8-44ce-b11d-acb71abf90c6" TYPE="ext4" 
/dev/sda2: UUID="7CBVuf-OmlK-2OnU-UVM0-O7nA-s8I3-zvOFKg" TYPE="LVM2_member" 
/dev/sda1: UUID="899895d5-6fb4-4c87-a761-65345e88174d" TYPE="ext4" 
/dev/mapper/vg_hallen4brxrc1-lv_swap: UUID="7450754c-e2a2-4516-b989-bfbb5e985de7" TYPE="swap" 
/dev/mapper/vg_hallen4brxrc1-lv_home: UUID="7aa466a7-ed56-4697-a228-086b2749f390" TYPE="ext4" 
# pvchange -u /dev/sda2
  Volume group containing /dev/sda2 has active logical volumes
  0 physical volumes changed / 1 physical volume not changed
# pvchange -u /dev/sda1
  Failed to read physical volume /dev/sda1
  0 physical volumes changed / 0 physical volumes not changed
# pvchange -u /dev/mapper/vg_hallen4brxrc1-lv_home
  Failed to read physical volume /dev/mapper/vg_hallen4brxrc1-lv_home
  0 physical volumes changed / 0 physical volumes not changed

Ser Olmy · 08-02-2013, 11:09 AM

Quote:

Originally Posted by cowmoo32

...

Code:

# blkid
/dev/mapper/vg_hallen4brxrc1-lv_root: UUID="d8e96ad4-45e8-44ce-b11d-acb71abf90c6" TYPE="ext4" 
/dev/sda2: UUID="7CBVuf-OmlK-2OnU-UVM0-O7nA-s8I3-zvOFKg" TYPE="LVM2_member" 
/dev/sda1: UUID="899895d5-6fb4-4c87-a761-65345e88174d" TYPE="ext4" 
/dev/mapper/vg_hallen4brxrc1-lv_swap: UUID="7450754c-e2a2-4516-b989-bfbb5e985de7" TYPE="swap" 
/dev/mapper/vg_hallen4brxrc1-lv_home: UUID="7aa466a7-ed56-4697-a228-086b2749f390" TYPE="ext4"

Clearly, your root device is /dev/mapper/vg_hallen4brxrc1-lv_root. That's the device with the file system which UUID you wish to change.

LVM Physical Volumes also have UUIDs, but they are not related to the file system at all. They are only used by the LVM subsystem, and have nothing to do with the UUID you can pass to the mount command or put in /etc/fstab as a device reference.