[LEAPSECS] Look Before You Leap ? The Coming Leap Second and AWS | Hacker News

[Joseph M Gwinn]

"LEAPSECS" <leapsecs-bounces at leapsecond.com> wrote on 05/19/2015 05:49:23
PM:

> From: "Eric R. Smith" <ersmith at hfx.eastlink.ca>
> To: Leap Second Discussion List <leapsecs at leapsecond.com>
> Date: 05/19/2015 06:19 PM
> Subject: Re: [LEAPSECS] Look Before You Leap ? The Coming Leap
> Second and AWS | Hacker News
> Sent by: "LEAPSECS" <leapsecs-bounces at leapsecond.com>
>
> On 19/05/15 05:39 PM, Joseph M Gwinn wrote:
> >> From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
> >> To: Leap Second Discussion List <leapsecs at leapsecond.com>, Hal
> >> Murray <hmurray at megapathdsl.net>
> >> Date: 05/19/2015 02:22 PM
> >> Subject: Re: [LEAPSECS] Look Before You Leap ? The Coming Leap
> >> Second and AWS | Hacker News
> >> Sent by: "LEAPSECS" <leapsecs-bounces at leapsecond.com>
> >>
> >> --------
> >> In message
> >> <20150519181135.CACBE406057 at ip-64-139-1-69.sjc.megapath.net>, Hal
> >> Murray writes:
> >>
> >>> I think the problem is conflicting standards.  POSIX doesn't agree
with
> > UTC.
> >>
> >> Not so much "doesn't agree" as "ignores".
> >
> > No, it's Doesn't Agree - the issue was very much debated.
> >
> > True UTC (with leap seconds) didn't cure a problem the committee cared
> > about, and managed to cause problems they did care about.  In short,
POSIX
> > systems have to be able to work in a cave, with no access to the sky or
> > knowledge of astronomy.
>
> If POSIX time_t were actually a count of SI seconds elapsed since the
> epoch, then a machine in a cave (with an accurate enough clock) could in
> principle maintain correct timestamps. As it stands though, POSIX time_t
> cannot be implemented without access to a UTC reference of some kind,
> i.e. access to the sky.

Well, while POSIX mentions SI seconds, the standard is careful to say that
these seconds are not exactly SI seconds (because UNIX workstations can
have pretty bad clocks).  And the standard specifically disclaims being
UTC, despite the appearance.  Read the standard carefully.  It is intended
and designed to support isolated operation.

Joe Gwinn
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