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Date: Mon, 20 Apr 2015 15:16:43 -0600
From: Eric Blake <eblake AT redhat DOT com>
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To: cygwin AT cygwin DOT com
Subject: Re: tar zxvf won't  work with Redhat generated compressed tar file
References: <COL130-W80F61D41DBC766A5C40206C2E00 AT phx DOT gbl>,<969800560 DOT 20150420222609 AT yandex DOT ru>   <COL130-W78804B6BA04135A92CC2FAC2E00 AT phx DOT gbl>,<509379965 DOT 20150420235036 AT yandex DOT ru> <COL130-W65B445CB84F1010DEEDA6EC2E00 AT phx DOT gbl>
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On 04/20/2015 03:08 PM, Murthy Gandikota wrote:

>>
>>> $ tar xvf mytar.gz
>>> tar: This does not look like a tar archive
>>> tar: Skipping to next header
>>> tar: Exiting with failure status due to previous errors
>>
>> Then what makes you think it is actually a tar archive?
>> What
>>
>> gunzip> mytar < mytar.gz; file mytar
>>
>> says?
>>

> Sorry, didn't notice the top-posting.... here is the  output to the comma=
nd
>=20
> mytar: gzip compressed data, last modified: Tue Mar 24 03:50:58 2015, fro=
m Unix

Then it looks like you have a DOUBLE-compressed file.  That is, someone
took a .tar.gz file, and ran THAT through gzip again (which seldom does
anything except make a LARGER file - because the first round of
compression removed any redundancy).  Tar cannot read a
double-compressed stream, but breaking things into two steps lets you
get back to a single compressed stream, where the tar call then
auto-decompresses because you weren't supplying an explicit 'z' the
second time around.  To prove it, try:

gunzip <mytar.gz >mytar
tar zxvf mytar

and if it still untars with an explicit decompression, then you have
proven that your original file was double-compressed.  Also, if I'm
right about double compression, then mytar.gz would likely be slightly
larger than mytar (rather than the usual case of the .gz being
noticeably smaller).

--=20
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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