[LEAPSECS] Leapseconds, more evidence

Zefram zefram at fysh.org
Mon Jul 2 18:00:55 EDT 2012

Rob Seaman wrote:

>but there are some interesting choices like 47 minutes after the hour,

I make a point of randomising the phase of all my cron jobs. Cron makes
it easy to schedule a job for the same time every hour or every day, so
I tend to use hourly or daily cycles but with a static random selection
of phase. E.g., my job to check for a new version of the Olson timezone
database runs at 7 minutes past each hour, because 7 is what came out
of "echo $((RANDOM%60))" (zsh) when I set it up. Another technique
I've seen is to put a random sleep first thing in the job's commands,
so that it's dithered per run.

>I was taken by the 17 minute cycle quoted for one of the issues

>in several reports (though perhaps borrowing from the same source).

>Anybody know what that was about?

That's ntpd. It uses power-of-two numbers of seconds for the pauses
between polls of each peer, and so tends to update tracking parameters
on that cycle. (It doesn't maintain a strict cycle time; you get an
approximate cycle dominated by that pause time.) It goes up to 1024 s,
which is 17 min + 4 s. "ntpq -c pe" shows the selected pause time for
each peer in the "poll" column.


More information about the LEAPSECS mailing list