[TriLUG] A question about using dd to restore a corrupt disk image

[Maarten Lippmann]

Thanks for the helpful responses, I'll forward them.

It makes me wonder what is in that file that was so previous it
warranted e-mailing a complete stranger.

Evil software the likes of which the world has never seen.
The source code to the new Debian Gnu/kWindows build, ready for
installation on a Beowulf cluster
of Raspberry Pi's and guaranteed to explode the heads geeks world wide.
Now we are all complicit.

On Thu, Apr 12, 2012 at 9:08 PM, Andrew Blum <ajblumx at gmail.com> wrote:
> On Thu, Apr 12, 2012 at 7:09 PM, Maarten Lippmann <m.w.lippmann at gmail.com>wrote:
>
>>
>>
>> He was wondering if there was any way of copying the contents of the
>> corrupt copy - everything _except_ the corrupt header into the working
>> copy or the
>> other way round.
>>
>> Simple visualization:
>> Corrupt file:
>> data1_data2_data3_Corruptheader
>>
>> Good older file:
>> data4_data5_data6_Goodheader
>>
>>
>>
> I'm not a storage recovery specialist, but he may want to try the seek
> option built into the dd command:
>
>       seek=BLOCKS
>              skip BLOCKS obs-sized blocks at start of output
>
> Does he know the exact position that separates the data from the header in
> the two files (like sector n and x below) ?
>
> Corrupt file:
> sectodata1_data2_data3_<sector n>Corruptheader
>
> Good older file:
> data4_data5_data6_<sector x>Goodheader
>
> If so, then try something like this (given with 512 Byte block size):
>
> # dd if=<corrupt_file> of=/tmp/file_data bs=512 count=<sector n>
> # dd if=<good_older_file> of=/tmp/file_header bs=512 seek=<sector x>
>
> # cat /tmp/file_header >> /tmp/file_data
>
> --
> Andrew
> --
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