Re: gunzip crc error :(

[Shing-Fat (Fred) Ma]

The exact error message comes after some few minutes gunzipping
to /dev/null :

     gunzip: mali.tgz: invalid compressed data--crc error

where mali.tgz is the tgz file.

It's not possible to unzip the whole thing and compare it with the
original because there is no tar file (it was piped in from tar).  The
sheer size of the file makes it impractical for me as a common user
to create unnecessary copies.  It also precludes unzipping it to tar,
and untarring it into a full file directory tree.  Besides, selected files
in my file system change day-by-day (second by second) merely
because I log in and use the facilities, so a comparison will definitely
turn up many discrepancies.

Lots of constraints.    Double :(  .

Fred

--
--------------------------------------------------------------------------
Fred Ma
Department of Electronics
Carleton University, Mackenzie Building
1125 Colonel By Drive
Ottawa, Ontario
Canada     K1S 5B6
address@hidden
==========================================================================

"Shing-Fat (Fred) Ma" wrote:

> Hi,
>
> gzip 1.3 *is* the second gzip implementation I'm using to create the
> archive and retrieve from it. The first was gzip 1.2.4, when the original
> problem was encountered.
>
> I'm pretty sure that the corruption is really in my tgz file.  I suspect the
> earlier gunzip would have been unable to look past the point of the
> corruption, whereas it seems that the new gzip can retrieve good data
> from the tgz file if it's far enough away from the point of corruption.
>
> Still, any suggestions of what to do about this would be greatly appreciated.
> It is a very disturbing feeling to have, that my nightly backups are
> corrupted.
>
> Fred
>
> --
> --------------------------------------------------------------------------
> Fred Ma
> Department of Electronics
> Carleton University, Mackenzie Building
> 1125 Colonel By Drive
> Ottawa, Ontario
> Canada     K1S 5B6
> address@hidden
> ==========================================================================
>
> Paul Eggert wrote:
>
> > > Date: Thu, 27 Sep 2001 00:20:13 -0400
> > > From: "Shing-Fat (Fred) Ma" <address@hidden>
> > >
> > > I installed gzip-1.3 and made sure it was the gzip being
> > > invoked.  Still getting the CRC error.
> >
> > This suggests that the compressed file is corrupted somehow.
> > Have you checked the same file with a different gzip implementation?
> >
> > > I extract the last file in the tgz archive, and it compares
> > > perfectly with the unarchived file.
> >
> > That's quite possible.  If the corrupted file expands to a tar image
> > that erroneous only in its data, the error might not be in the last
> > file -- and it might even be in a place in the tar image that does not
> > correspond to any file, and is therefore harmless.
> >
> > > The gzip FAQ said that
> > > gzip would eventually have error recovery features allowing
> > > it to retrieve files past the point of a CRC error in a tgz file.
> > > Maybe this is it.  Either that, or the warning is benign.
> >
> > or you really have a bad file.  All of these are possible.
> >
> > > In particular, tar removes the "/" from "/var/mail/fma".  Maybe it
> > > tries to go backward in the tar file to do this.
> >
> > No, tar doesn't do that.
> >
> > > Since there is no actual tar file, could it possibly be messing up
> > > the tgz file?
> >
> > No.