From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andrew Gierth <andrew@tao11.riddles.org.uk>
cc: Stephen Frost <sfrost@snowman.net>, Robert Haas <robertmhaas@gmail.com>,
        Alvaro Herrera <alvherre@2ndquadrant.com>,
        Andres Freund <andres@anarazel.de>, Christoph Berg <myon@debian.org>,
        PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: UCT (Re: pgsql: Update time zone data files to tzdata release
 2019a.)
In-reply-to: <87y31wytdl.fsf@news-spur.riddles.org.uk>
References: <20190620161400.6wtuybv64ihnfy6d@alap3.anarazel.de>
 <20190620172838.GA21945@alvherre.pgsql>
 <CA+TgmobK3TVoxNJ0vCwvLcAjjaLvMLFWcbEpWA042bT9VdVWfQ@mail.gmail.com>
 <20190620182406.GD2480@tamriel.snowman.net>
 <87y31wytdl.fsf@news-spur.riddles.org.uk>
Comments: In-reply-to Andrew Gierth <andrew@tao11.riddles.org.uk>
	message dated "Thu, 20 Jun 2019 20:19:24 +0100"
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Date: Thu, 20 Jun 2019 17:59:56 -0400
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Andrew Gierth <andrew@tao11.riddles.org.uk> writes:
> Tom's "fix" of backpatching 23bd3cec6 (which happened on Friday 14th)
> addressed only a subset of cases, as far as I know working only on Linux
> (the historical convention has always been for /etc/localtime to be a
> copy of a zonefile, not a symlink to one). I only decided to write (and
> if need be commit) my own followup fix after confirming that the bug was
> unfixed in a default FreeBSD install when set to UTC, and there was a
> good chance that a number of other less-popular platforms were affected
> too.

I think your info is out of date on that.

NetBSD uses a symlink, and has done for at least 5 years: see
set_timezone in
http://cvsweb.netbsd.org/bsdweb.cgi/src/usr.sbin/sysinst/util.c?only_with_=
tag=3DMAIN

macOS seems to have done it like that for at least 10 years, too.
I didn't bother digging into their source repo, as it's likely that
System Preferences isn't open-source; but *all* of my macOS machines
have symlinks there, and some of those link files are > 10 years old.

I could not easily find OpenBSD's logic to set the zone during install,
if they have any; but at least their admin-facing documentation says to
create the file as a symlink:
https://www.openbsd.org/faq/faq8.html#TimeZone
and there are plenty of similar recommendations found by Mr. Google.

In short, I think FreeBSD are holdouts not the norm.  I note that
even their code will preserve /etc/localtime's symlink status if
it was a symlink to start with: see install_zoneinfo_file in
https://github.com/freebsd/freebsd/blob/master/usr.sbin/tzsetup/tzsetup.c

			regards, tom lane