On Wed, Dec 06, 2023 at 05:40:00PM -0000, Curt wrote:
POSIX format specification
The POSIX time zone format is the traditionally used format for AIX systems and
provides a slight performance advantage over the Olson time zone format.
Example of a POSIX format is EST5EDT.
The advantage of POSIX is that you can easily and explicitly specify the time
zone and daylight saving time (DST) details manually, however you wish. The
performance of applications that call time functions will be faster than using
Olson specification. And whenever a nation's government decides to change its
DST rules, the POSIX format is simpler because we can simply change the
variable definition. There is no need to install any new patch to update time
database files, as Olson requires.
Does this apply to "us?"
https://developer.ibm.com/articles/au-aix-posix/
This does *not* describe how Debian's EST5EDT, and similarly named
zones, work. Debian's time zones use a database of DST transition
periods -- all of them, even EST5EDT. It's just a different set of
transitions than America/New_York uses.
Also, you snipped the rest of that section:
The disadvantage of this approach is that it cannot track the history
of timezone-related changes and it is not easy to read as it looks
cryptic. When a government changes the rules and you update your time
zone (TZ) variable, it is assumed to be the same DST rule for all
years past and future.
That's a fairly important paragraph.
Applying the same rules to a timestamp in 2023 and a timestamp in 2006
may give incorrect results, as the DST rules in the US changed in 2007.
That's why the method described by this AIX manual is no longer in
common use.