Re: /etc/localtime and How it Works
- Date: Tue, 12 Jun 2018 14:10:07 -0400
- From: Dan Ritter <dsr@xxxxxxxxxxxxxxxx>
- Subject: Re: /etc/localtime and How it Works
On Tue, Jun 12, 2018 at 12:38:05PM -0500, Martin McCormick wrote:
> I was expecting America/New_York to look just like
> America/Chicago except for the UTC offset and maybe some slightly
> different dates back when DST was mostly used on the coasts and
> not at all in much of the middle of the country.
> Oklahoma and Texas, for example, didn't use any time
> shifting except for War Time until 1967 after passage of the
> Uniform Time Standards Act and a decision by all the major
> television networks of the day to no longer send delayed
> broadcasts down their wires to affiliates in states that didn't
> observe DST.
> So, my question is why is there such a difference between
> the two files and how do people in the Eastern Time Zone
> automatically learn of the two time shifts each year?
You have just stepped into a minefield. It's a really
interesting one, though.
First: the compilation of timezone data is the Olson Database,
after the original editor. The current editor is Paul Eggert,
and the America/New_York style nomenclature is his fault.
Second: every decision recorded in the Olson Database is a
political decision. Science and engineering don't really
enter into it much.
In many countries, the national government sets the standard,
and that's that. In the USA, the federal government sets the
dates for changing from standard to daylight saving time and
back, but does not mandate adoption of DST or any specific
You'd think that at least each state would be consistent
internally, but that's not necessarily the case either.
So, to answer your question: laws are passed and the information
published in the same way that other laws are published, plus
newspapers and TV news and so forth tend to be vocal about the
issue. And Eggert learns about it and puts it in the database,
and then everybody makes changes to their copies of tz.