Leap seconds

Gary E. Miller gem at rellim.com
Sun Jan 14 20:51:45 UTC 2018

Yo Paul!

On Sun, 14 Jan 2018 12:33:03 -0800
Paul Theodoropoulos <paul at anastrophe.com> wrote:

> I am confused about leapseconds. My understanding is that this
> confusion is not an unusual state. :)


> I'm running a Raspberry Pi 1 Raspian Stretch Stratum one server,
> built to the spec of the Stratum-1-Microserver HOWTO on the
> ntpsec.org site.


> The example/suggested ntp.conf file in that document
> makes no mention of leapseconds.
> https://docs.ntpsec.org/latest/ntp_conf.html lists the leapfile
> directive, but the ntp.conf manpage does not, only mentioning it in
> regard to crypto functions. Though both mention the leapsmearinterval
> directive, making clear not to run that on a public server.


> Among the tools included with the NTPsec suite is ntpleapfetch, which 
> would imply (to me at least) that this is a task that should be 
> performed - though I'm also unclear on appropriate intervals. Perform
> it one minute before midnight on June 30 and Dec 31? Check monthly on
> the rare possibility of a leapsec at some other time?

From the ntpleapfetch man page:

       "This can be run as a cron job. As the file is rarely updated, and
       leap seconds are announced at least one month in advance (usually
       longer), it need not be run more frequently than about once every
       three weeks."

> So, I'm confused. Should I employ ntpleapfetch from cron and include
> the leapfile directive in my ntp.conf? Or is it best to exclude all
> of this on a public NTPsec server?

Depends on how connected your ntpd is to the rest of the world.  An
isolated ntpd needs to have a local leapfile.  An ntpd talking to
well managed NTP servers will get the leap notifications also from
those chimers.

BUT, against the standard, some NP chimers will be doing ugly thinsg
to the time they provide around the leap decond moment.  They may
be smearing time in odd ways.  Ways that will confuse your ntpd.

> I'm interested in conforming to best-practices.

Sadly, the concensus on best-practices does not exist.  For example,
Google does leap smearing:


And, just to add confusion, they used to smear over 24 hours, but
recently they smeared over 20 hours.

Alternatively, Amazon and Microsoft still smear over 24 hours.  Fun!

Now you can avoid those idiots, but do you know which of your chimers
are using those idiots as chimers?

So, if exact time around the leap second moment is important to you, best
to run a local GPS, with current leapfile and stay up for the New Year.

Or, just do not do anything that requires accurate time for 24 hours
before and after the leap secnd moment.  Go party!  :-)

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin
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