Re: NTP leap second question

[john stultz <johnstul@us.ibm.com>]

On Wed, 2005-09-14 at 11:39 -0700, George Anzinger wrote:
> It appears that a leap second is scheduled.  One of our customers is 
> concerened about his application around this.  Could one of you NTP 
> wizards help me to understand NTP a bit better.

First: I'm not an NTP wizard by any means, but I'll see if I can't help.

> First, I wonder if we suppressed the leap second insert and time then 
> became out of sync by a second, would NTP "creap" the time back in sync 
> or would the one second out of sync cause it to quit?

The ntpd's slew-bound is .125s I believe, so a second offset would cause
ntpd to adjust the time using stime()/settimeofday(). You could run ntpd
with the -x option which forces it to always slew the clock. This
however could cause the initial sync to take quite some time.


> Assuming NTP would do the "creap" thing, is there a way to tell NTP not 
> to insert the leap second?

If I recall, leapsecond implementations are a pretty contentious issue.
Some folks have suggested having the kernels note the leapsecond and
slew the clock internally. This sounds nicer then just adding or
removing a second, but I do not know how that would affect synchronizing
between a number of systems. So I'll defer the larger discussion to the
real NTP wizards.