[tz] [Tzdist-bis] [calsify] tzdist and IANA

Martin Burnicki martin.burnicki at meinberg.de
Thu Jul 18 14:05:13 UTC 2019

Luigi Rosa wrote:
> Daniel Migault wrote on 18/07/2019 15:07:
>>      >> Wouldn't it be nice to have an infrastructure similar to what
>> the NTP
>>      >> pool provides for time synchronization?
> My two cents of an admin of hosts (mainly Windows) that travel back and
> forth thru the seven seas (namely Cruise ships).
> Short version: TZ sync is a pain in the arse.


> Long version.
> You cannot use UTC for all the hosts because, for instance, some of them
> show information to the guests or are used to manage crew shifts (always
> expressed in ship time).
> > On some ships the so called "master clock" has two NTP servers: one
> "classic" UTC and the other with ship time.

Yep. We had a customer (a cruise line) who received this solution from us.

The main problem was that there were dumb date/time displays for the
passengers which display whichever time they receive from the NTP
server, without applying any offset.

So the solution was to install an extra NTP server which provided UTC +
a configurable offset for the clocks visible to passengers. And the
local time offset to be applied to UTC had to be reconfigured whenever
the ship enters a region with a different time zone. Of course this is
an evil workaround for limitations of the time displays.

Formerly there were clocks that were controlled by an IRIG time code
signal which could transport lo time instead of UTC. I'm assuming the
folks who developed these dump NTP clocks simply replaced the time code
receiver by a network port, without keeping in mind that NTP has been
designed to transport UTC only, not local time.

For such dump time displays even the tzdist protocol probably won't help
much. Only if the displays know about time zones the zone rules could be
updated via the network, but still you had to tell each display *which*
zone to use if the ship moves from one region to the next.

> We cannot use ship time NTP server because NTP clients (correctly)
> assume that NTP is about UTC, while the local time is just a "logical
> view" of NTP. If we sync Windows hosts with ship time the result is a
> mess (somebody said "Kerberos"?).

Of course.

> We concocted a simple way to sync TZ between Windows hosts.
> The "TZ Server" runs the command
> tzutil /g > c:\tz\tz.txt
> C:\tz is shared as TZ
> Every client issue the commands
> tzutil /s "%TZ%"
> The procedure is tested on Win2016, 2012R2 and Win10
> Detailed info in my blog article:
> https://translate.google.com/translate?sl=it&tl=en&u=https%3A%2F%2Fsiamogeek.com%2F2019%2F06%2Fsincronizzare-la-time-zone%2F
> The original is in Italian:
> https://siamogeek.com/2019/06/sincronizzare-la-time-zone/

Thanks for these interesting pointers.

Martin Burnicki

Senior Software Engineer

MEINBERG Funkuhren GmbH & Co. KG
Email: martin.burnicki at meinberg.de
Phone: +49 5281 9309-414
Linkedin: https://www.linkedin.com/in/martinburnicki/

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