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Re: [Bug-tar] Re: AMTAR brokenness

From: Sergey Poznyakoff
Subject: Re: [Bug-tar] Re: AMTAR brokenness
Date: Fri, 16 Apr 2004 10:27:15 +0300


Actually I was planning to address this issue a bit later, since I
do not have a solution for automake yet. Anyway: 

Alexandre Duret-Lutz <address@hidden> wrote:

>  Roger> +     $(AMTAR) chf - $(distdir) --format=posix | GZIP=$(GZIP_ENV) 
> gzip -c >$(distdir).tar.gz
> [...]
> Sorry for the late comment.  I can see at least three reasons
> against this patch:

I agree with all three. The format used for distribution tarballs should
be a reasonably old one, so that any existing version of tar be able to
cope with it. 

On the other hand, let me notice that the current practice of using
(so called) V7 format for make dist falls within the first reason you

> The --format=posix options is a GNU Tar option, which means `make dist'
> can no longer be run with other make implementations.  Automake makefiles 
> should be portable and this breaks it.

The -o option used by automake is as well a GNU Tar option, and it
has another meaning for other tar implementations. According to
POSIX specs, -o stands for 'Assign to  extracted  files  the  user
and group  identifiers  of  the  user running the program', i.e.
it corresponds to GNU tar --no-same-owner option. Let's take as
examples two other tar implementations:

1) Sun tar. Its manpage says:

     o     Ownership. Assign to  extracted  files  the  user  and
           group  identifiers  of  the  user running the program,
           rather than those on  tarfile.

2) Star:

     -nochown, -o
           Do  not restore owner and group of files.  This may
           be used if super  user  privileges are  needed  to
           overwrite existing files but the
           local ownership of the existing files should not change.

Thus, using -o in Makefiles is at best irrelevant to creation of

Returning to the question which format should be chosen for
distribution tarballs: I would recommend the 'ustar' format.
It also has a limitation on the maximum length of stored pathnames,
but the limitation is 256 characters, which is reasonably large.
Besides, ustar archives can be read by any existing implementation
of tar.


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