REMINDER: LEAP SECOND

[mhuff at ox.com (Matthew Huff)]

A backward step is a known issue and something that people are more comfortable dealing with as it can happen on any machine with a noisy clock crystal.

Having 61 seconds in a minute or 86401 seconds in a day is a different story.

> On Jun 23, 2015, at 8:37 PM, Harlan Stenn <stenn at ntp.org> wrote:
> 
> 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