On 2025-12-28 19:12, Paul Eggert via tz wrote:
On 2025-12-28 10:59, Paul Gilmartin via tz wrote:
ISTR on Linux long ago, a subdirectory,
/usr/share/zoneinfo/right,
which used arguments not POSIX time but TAI.
Was that a local hack, or was it removed,
possibly because of uncertainty of future
leap seconds?
It's still there, as a rarely-used option. By default current TZDB installs two
files for Los Angeles:
/usr/share/zoneinfo/America/Los_Angeles
/usr/share/zoneinfo-leaps/America/Los_Angeles
and the latter file uses TAI. You can change the installation default by using
'make REDO=posix_only', 'make REDO=right_only', or 'make REDO=right_posix'; see
the Makefile.
Many platforms, like Debian, use an older directory organization, which puts the
two Los Angeles files here instead:
/usr/share/zoneinfo/America/Los_Angeles
/usr/share/zoneinfo/right/America/Los_Angeles
/usr/share/zoneinfo/posix/America/Los_Angeles
where the first two names resolve to the same file (or to files with identical
contents).
An advantage of the older approach is that one can use 'TZ="right/America/
Los_Angeles" to get TAI. A disadvantage is that functions like gmtime no longer
work the way people expect; for example, TZ='right/America/Los_Angeles' gets you
localtime with leap seconds, but gmtime without leap seconds, which leads to
nonsense like this with GNU date:
$ export TZ=right/America/Los_Angeles
$ format='%Y-%m-%d %H:%M:%S %::z (%Z)'
$ date "+$format"; date -u "+$format"
2025-12-28 18:04:48 -08:00:00 (PST)
2025-12-29 02:05:15 +00:00:00 (UTC)
so the timestamps make it look like Los Angeles is 8 hours and 27 seconds behind
UTC, even though the difference is correctly reported to be 8 hours exactly.
This confusion breaks some applications.
This is why TZDB 1998e changed to something more like the current approach; see
commit 77e3dfe1a7b7e14e9f252fc628a5d405c35b6444 dated 1998-05-25 13:04:43 -0400
in the development repository. Effectively this means the TAI TZif files are
inaccessible unless you use full pathnames in TZ, which I hope means you know
the trouble you're getting into.
Perhaps it is time to change the default REDO value in the Makefile to
REDO='posix_only', as REDO='posix_right' isn't being used much and when it is
used is probably being used incorrectly. Such a change to the default wouldn't
affect platforms like Debian that continue to use the pre-1998 approach.
Fedora, OpenSuSE and related distros release tzdata{,-posix,-right} under
zoneinfo/{,posix,right}:
https://src.fedoraproject.org/rpms/tzdata/blob/f43/f/tzdata.spec
Debian and related release TAI including Etc/GMT[-+][0-9]+ in tzdata-legacy
under zoneinfo/right.
--
Take care. Thanks, Brian Inglis Calgary, Alberta, Canada
La perfection est atteinte Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter not when there is no more to add
mais lorsqu'il n'y a plus rien à retrancher but when there is no more to cut
-- Antoine de Saint-Exupéry
