On Tue, Apr 16, 2024 at 01:25:33PM -0600, Todd C. Miller wrote:
> On Tue, 16 Apr 2024 13:16:17 +0200, Jeremie Courreges-Anglas wrote:
> 
> > I'd like to move fast and switch the default in tar(1) as soon as
> > tar(1) provides the user with an option to go back to ustar if really
> > needed.  I hope people are fine with that.
> 
> Do you know which format other versions of tar use by default?

I'm not sure whether you're talking about defaults for writing, or
defaults for reading.  I would expect most implementations to do their
best to detect and accept pax and possibly other less standard
formats when reading.

For writing archives, GNU tar uses the GNU format, python uses pax,
bsdtar apparently uses a variant of pax without atime/mtime (a idea I
had in mind).  Solaris apparently still uses ustar for tar(1).

> How does this affect interoperability with older versions of tar?

File whose names fit in ustar headers should be restored correctly,
except for the missing information from the extended header ofc.  Some
implementations unaware of the pax format might write the extended
header records as a regular file in a path/PaxHeaders.%p/file instead
of ignoring them.

https://mgorny.pl/articles/portability-of-tar-features.html#extended-file-metadata

has more information.

-- 
jca