recovering partially corrupt data

[Udo Rader]

hi out there,

first let me point out that I know very well that I am very probably
sending this question to the wrong place (address@hidden), but it is a
major issue to me and very probably to many other users out there as
well. The only potential "bug" I see in the whole issue is that I did
not find any other place to report my problem to, there is no
"address@hidden" list or something and that the documentation is kind
of vague on how to retrieve corrupted data ...

But my problem looks as follows:
Some time ago I had to backup some data (most of all home-directories)
and thus used tar xjf foo.tar.bz /home/foo to create nice backup files,
the two largest of more than 200MB size.

When I now try do restore the data, I end up with tar telling me this:
-----------CUT-----------
bzip2: Data integrity error when decompressing.
        Input file = (stdin), output file = (stdout)

It is possible that the compressed file(s) have become corrupted.
You can use the -tvv option to test integrity of such files.

You can use the `bzip2recover' program to *attempt* to recover
data from undamaged sections of corrupted files.

tar: 56 garbage bytes ignored at end of archive
tar: Unexpected EOF in archive
tar: Unexpected EOF in archive
tar: Error is not recoverable: exiting now
-----------CUT-----------

So far so good, I then used - as suggested - bzip2recover to get at
least some information and ended in getting hundreds of small bz2 files
each containing 900K of data. And every time I only found *one* single
900K file that had compression-errors ...

And no matter how hard I try, even a "forced" erratic decompression does
not make tar happy.

sample unhappiness:
-----------CUT-----------
tar: This does not look like a tar archive
tar: Skipping to next header
tar: Archive contains obsolescent base-64 headers
tar: 497 garbage bytes ignored at end of archive
tar: Error exit delayed from previous errors
-----------CUT-----------

My question in general is the following: Is it possible for tar to
access data stored "in the middle" of a tar-file if the tar file
contains some garbage data in the beginning? If not, I am really
desperate, as I have some files with more than 200MB of data and I am
not able to access most of the data because the first tenth of the file
contains some (<1MB) garbage ...

If anybody can give me some information how to get back the data, I
would be ***very*** grateful. And if again somebody should feel annoyed
about my posting, **please** be so kind to point me to the right place
where I can ask such things.

Thanks anyway for the great work you are doing at gnu.org.

a very desperate Udo Rader