I have a Synology NAS with a RAID 1 setup on which I recently accidentally deleted a shared folder with data I want back. I shut down the NAS and booted into a machine with an Ubuntu Live Cd and attached one of the NAS drives.

I made an image of the drive using DD and now have an oldhd.img file on an external drive.

I then moved to a new machine, booted up with the Live CD attached the external drive and changed to the external drive directory and ran this command

mount -r -o loop oldhd.img /mnt

Then I ran fdisk -l and saw the drive I need to be recovered was /dev/sdb

I changed dir to my computer's hard drive folder and ran:

extundelete /dev/sdb --restore-all

It returns :

extundelete - failed to read-only open device "/dev/sdb": Error code 2133571347

What am I doing wrong? And what should I do instead?

  • Ok so I created an image of the entire disk, not a copy of the file system. So in this case I read I must specify offset options for losetup? How to do this? – Gene Mills Nov 22 '14 at 13:10

When you use mount with the -r option, the filesystem is mounted read only. In order to do any writing to the disk you must not mount in read only.

So, the command should be

mount -o loop oldhd.img /mnt

Also, from a sourceforge forum post:

Error code 2133571347 is "EXT2_ET_BAD_MAGIC" This means there is no valid signature for the superblock.


  • The superblock is corrupt, in which case you can try to open the file system with help of the superblock copies. see options -b blocknumber and -B blocksize, or
  • You have made ​​a mistake during the creation of the file system image, or
  • You have created an image of the entire disk, not a copy of the file system, in which case you must specify offset options for losetup.
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