REMINDER: LEAP SECOND

[stenn at ntp.org (Harlan Stenn)]

shawn wilson writes:
> On Jun 23, 2015 6:26 AM, "Nick Hilliard" <nick at foobar.org> wrote:
> >
> 
> >
> > Blocking NTP at the NTP edge will probably work fine for most situations.
> > Bear in mind that your NTP edge is not necessarily the same as your
> network
> > edge.  E.g. you might have internal GPS / radio sources which could
> > unexpectedly inject the leap second.  The larger the network, the more
> > likely this is to happen.  Most organisations have network fossils and ntp
> > is an excellent source of these.  I.e. systems which work away for years
> > without any problems before one day accidentally triggering meltdown
> > because some developer didn't understand the subtleties of clock
> monotonicity.
> >
> 
> NTP causes jumps - not skews, right?

Left to its default condition, ntp will step/jump a change in excess of
128msec.

If you want to slew the clock instead, a 1 second correction will take a
little over 33 minutes' time to apply.

I don't understand why people believe that stopping ntpd for a few
minutes while the leap second is applied will help.  If the system clock
keeps good time, it will *still* be about 1 second ahead when ntpd is
restarted, and that will trigger a backward step which is fatal to a
number of applications.

H