On Thu 2020-11-12T18:13:54-0800 Guy Harris hath writ:
So what POSIX says in section 3 "Definitions":
https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html
is
3.150 Epoch
The time zero hours, zero minutes, zero seconds, on January 1, 1970 Coordinated Universal Time (UTC).
and what it says in section A.3 "Definitions" of the Rationale:
https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xbd_chap03.html
is
Epoch
Historically, the origin of UNIX system time was referred to as "00:00:00 GMT, January 1, 1970". Greenwich Mean Time is actually not a term acknowledged by the international standards community; therefore, this term, "Epoch", is used to abbreviate the reference to the actual standard, Coordinated Universal Time.
Although not specified by any standards nor recommendations, the term "Coordinated Universal Time" did then exist within the time service bureaus, and that has a precise meaning, and because Germany had not yet moved to stop broadcasting old UTC it was a legal time everywhere. It is also the case that the calendar day based on the rotation of the earth is not acknowledged by the international standards community, but at no point have the committees had the balls to create a recommendation or standard which changes the definition of the calendar day such that it is unrelated to the rotating earth. Such an action would violate national laws. This is the reason we have leap seconds. It is also the case that the CGPM, overseeing the SI, has never abrogated the definition of the mean solar second as 1/86400 of the calendar day. This is because they never defined it as such, so they cannot undefine it as such. In most places other than Germany (where it was deemed explicitly illegal) the mean solar second still has legal existence distinct from the SI second.
Should there be a request for clarification of what they mean by that?
No, mostly because of https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag... where POSIX has the word "approximates" and the phrase "relationship with the current actual time is implementation-defined." Also because that goes down the rabbit hole into places where the writers of the official (and, upon inspection of the source documents, pedantically incorrect) definitions for the time scales we use dared not go lest they give national bureaucrats clues about how there are two qualitatively different meanings for "time". -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m