On Mon, Dec 19, 2016 at 02:06:46PM -0600, Michael Scherer wrote:
> We're presently using the SOCK driver with chrony, and I wanted to verify
> the correct usage of the leap parameter.

> As far as I can tell, setting leap to 1 will schedule the insertion of a
> leap second, and won't apply it until the last day of June or December.


> Is there an expected minimum amount of time in advance that this
> needs to get set?

It depends on the polling interval of the SOCK refclock and whether
it is a server that will announce the leap second to its clients.
There needs to be at least one update of the system clock before the
actual leap second in order to be handled and there is a 5-second
interval around midnight where new measurements are ignored. If you
use the default 16-second polling interval for the SOCK refclock, the
refclock is reliably working and is always selected (i.e. has * in the
sources report), and there are no clients that would need to be
informed, something like 30 seconds before midnight should be enough.
If there are some NTP clients, possibly including an ntpd using 1024
second polling interval, it should be at least two hours.

> Does it matter if we keep that set after the leap second should be
> applied, so long as it gets cleared before the next schedule window?

No, that's fine. You have 6 months to unset the leap bits. chronyd as
a server will stop announcing the leap second immediately after
midnight, even if its sources didn't turn it off yet.

Miroslav Lichvar

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