Re: [chrony-users] Nanosecond precision with refclock SOCK

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Mon, Jan 15, 2024 at 06:57:48PM +0700, James Clark wrote:
> In computing the initial step, how does chrony handle leap seconds?
> 
> There are two ways of computing offsets:
> - subtracting the TAI times (so that it is really the number of seconds
> that elapse between the system time and the true time)
> - subtracting the POSIX times (so leap seconds are ignored)

chronyd corrects the system clock, which ignores leap seconds, so it
expects the second approach. It doesn't do any corrections of the
offset.

> > The leap should be set until the leap happens, starting up to 24 hours
> > before.
> >
> 
> What does "until the leap happens" mean exactly? Does that mean that adding
> the offset to the system time gives a time that is < 24:00:00 on the day of
> the leap second (i.e. the leap second is over)? Or is it until the leap
> second starts?

Until the leap is finished from the point of the reference clock, i.e.
the leap bit should be cleared after when the day changes in the
reference time (UTC).

In practice, it doesn't have to be so exact. chronyd ignores any
measurements made in or pointing to a 10-second interval around the
leap. At 23:59:55 it stops updating the clock and coasts through.

-- 
Miroslav Lichvar


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