Re: [Bug-ddrescue] What to do with created file?

[Ariel]

On Wed, 23 Feb 2005, Dennis wrote:

> Hi!
>
> I am quite new to ddrescue and now, I am facing a little problem.
>
> I did run ddrescue over the partition which contains my /home-path (as root)
> and got an output file which seems to be the correct size (about 30GB).
> But what to do with this file? After what I've read, ddrescue writes source
> devices back into files which are supposed to be a device, which should mean
> that I can simply mount the output file and then access the files in there.
> But this does not work!

Yes, normally you just do mount -o loop filename mountpoint

> Additionally, I have to add that my /home-partition is an encrypted loop
> device, but at the time I started ddrescue to backup this partition, it was
> mounted correctly and therefor accessible without limitations.

This makes it complicated. Even when it's mounted the partition itself is
still encrypted. What's not encrypted is the loopback. Try running the
command losetup -a when your home is mounted and you will see. What
happens is you are putting an encryption loopback over the partition, and
then mounting the loopback.

What you can try to do is run ddrescue on the loopback itself rather then
the partition, but you are not likely to get good results. Decryption will
be messed up if there are bad blocks, and when ddrescue retries the block
it may not give the same results as before, depending on where the error
is. (Also make sure the mount is mounted read-only. Copying a partition
mounted read-write is a bad idea.) If you do this, you must make sure
ddrescue uses the same block size as the encryption block size.

Best bet is to copy the partition (which you did), then put a decryption
loopback on top of the resulting output file, then mount that loopback.

Normally it's losetup -e whatever_encryption_you_use /dev/loop(some_number) 
file_name

Then mount the /dev/loop(number) someplace. Probably run e2fsck on it
first.

If this doesn't work I would need more details of how you are doing the
loopback encryption. You might want to email a loopback encryption mailing
list. Tell them you have a (partially damaged?) image of partition, and
ask how to decrypt it. Make sure you detail how you normally mount it, so
they know what encryption you are using.

        -Ariel

PS. Good luck, this may not be easy. BTW you never mentioned how bad the
damage to the partition was.