Subject: Re: FYI: upgrading GNU tar
To: Eric Haszlakiewicz <>
From: Greg A. Woods <>
List: current-users
Date: 10/14/2002 16:17:43
[ On Monday, October 14, 2002 at 10:39:22 (-0500), Eric Haszlakiewicz wrote: ]
> Subject: Re: FYI: upgrading GNU tar
> On Mon, Oct 14, 2002 at 11:08:23AM -0400, gabriel rosenkoetter wrote:
> > On Mon, Oct 14, 2002 at 02:37:17AM -0600, Rick Kelly wrote:
> > > So, pax can't really replace GNU tar...
> > > 
> > > Think of all the thousands of NetBSD backup tapes that were done with
> > > GNU tar.
> > 
> > Oh, the agony! Those people will have to use pkgsrc to recover from
> > their dated tapes!
> 	Well, maybe you could deal with it, but I know I'd be pretty pissed off
> if the "tar" command from a more recent version of NetBSD couldn't deal with
> archives created by an older release.  My first thought in that situtation
> probably wouldn't be "gee, I guess they took some features out".  It would
> be "oh shit, my backup is corrupted".

It's really not that big of a problem folks, as a little bit of testing
and research will easily reveal.  There's lots of discussion of the
various issues in the "GNU `tar' and POSIX `tar'" section of the GNU Tar
manual, but it boils down to a question of whether or not you've got any
files with really long names (>100 chars) or not.  I would think that
most people don't -- certainly that's true of archives I've found on the

Continuing down the GNU Tar path really only takes NetBSD further away
from being compatible with POSIX compliant systems in terms of both
archive formats and command-line use.  Newer GNU Tar versions are no
better at making portable archives than the now aged one that created
all your older backup tapes (the GNU folks really cornered themselves
badly on this one).  It's bad enough that it has gone on this long,
especially since there was not for the longest time out-of-the-box
access to the GNU Tar documentation including the section above, and
neither any clear notice to NetBSD users that they really need to use
'-o' (--portability) to get truly portable archives out of NetBSD "tar"
since what GNU Tar claims are "POSIX" format archives really are not at
all that compliant and are not even compatible out on the corner cases.

If anyone can provide evidence of a non-incremental archive created by
"tar" on any older NetBSD release that wouldn't be readable by "pax"
then I'll help write whatever fixes are necessary to help "pax" deal
with the archive.  I don't expect this to be a very common problem
though, but only other users can say one way or another.

(Support for the non-portable old and new GNU "incremental" formats is
something best left to GNU Tar itself -- pax need only recognize these
formats point users at GNU Tar instead of failing in some non-safe
manner.  Indeed even any incompatible "normal" GNU Tar format archives
might best be handled simply by recognizing the problem and deferring to
GNU Tar itself.)

								Greg A. Woods

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