Re: ntpsec as server questions
On 06/12/2023 12:22, David Wright wrote:
On Tue 05 Dec 2023 at 23:37:31 (+0700), Max Nikulin wrote:
I am surprised that POSIX EST5EDT timezone has irregularities at least
as it is implemented in GNU libc. I believed that it specifies just
standard and summer time.
During WWII they had War Time, just as Britain had Double Summer Time,
with Summer Time through the winters.
I was aware of special DST rules during WWII, but I did not expect that
"EST5EDT" may include any historical data. Certainly it does not
explicitly specify days when summer time is effective, just
abbreviations "EST" and "EDT" with time offset of 5 hours behind UTC for
"EST". Partial time transition history is new for me for these kind of
time zones.
https://en.wikipedia.org/wiki/Daylight_saving_time_in_the_United_States
is a long enough article.
I don't know who maintains the legacy EST5EDT zone, or for whom;
the quotation below suggests that it may just follow New Jersey.
For a long period after the war, it seems the timezones in the US
were all over the place.
https://data.iana.org/time-zones/theory.html :
Older versions of this package defined legacy names that are
incompatible with the first guideline of location names, but which are
still supported. These legacy names are mostly defined in the file
'etcetera'. Also, the file 'backward' defines the legacy names
'Etc/GMT0', 'Etc/GMT-0', 'Etc/GMT+0', 'GMT0', 'GMT-0' and 'GMT+0', and
the file 'northamerica' defines the legacy names 'EST5EDT', 'CST6CDT',
'MST7MDT', and 'PST8PDT'.
[...]
POSIX does not define the DST transitions for TZ values like "EST5EDT".
Traditionally the current US DST rules were used to interpret such
values, but this meant that the US DST rules were compiled into each
time conversion package, and when US time conversion rules changed (as
in the United States in 1987 and again in 2007), all packages that
interpreted TZ values had to be updated to ensure proper results.
My reading of this document is that EST5EDT file in tzdata is a POSIX
extension, not "true" POSIX.
A lot of details concerning database contents are given if files like
https://github.com/eggert/tz/blob/main/northamerica
I have not noticed any America/* timezone that strictly follows EST5EDT.
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