Re: [PATCH] change default --format from gnu to posix

[Paul Eggert]

On 12/13/21 21:56, Mike Frysinger wrote:

> for automake, the limitations in the default v7 catch people off guard (like
> filename limits).

This is a good reason to switch formats. That being said, a downside of 
--format=pax is that it gratuitously uses pax extensions when not needed 
by the uses of 'tar' that we're talking about. These pax extensions can 
cause trouble, as illustrated by Michał's analysis.

This discussion suggests the need for a new, easy-to use format option, 
which is like '-Hpax' except that it omits atime and ctime, and omits 
the subseconds part of mtime. Using this format would mean that pax 
extensions won't be used unless they're needed (a file with a long name, 
a timestamp past the year 2246, etc.) and so the tarball would be more 
portable to platforms with older or buggy tarball extractors.

Maybe we could call this the 'art' format, for "archive reproducible 
tarball", so that people could use 'tar -Hart' for it. Like 'ustar', 
'art' format would be a strict subset of 'pax' format so it would be 
POSIX-conforming.

We could introduce the new option in the next release of GNU tar, and 
think about changing the default format to it in a later release.

What do you think?