[ntp:questions] Nontrivial time adjustments

Danny Mayer mayer at ntp.org
Wed Jun 10 03:29:11 UTC 2009

Алексей Иванов wrote:
> Hello.
> I have a question inspired by a problem on my work.
> I work at a regional Russian broadcasting company. We broadcast in our
> region by replacing several state programmes with regional ones. All the
> rest time we just relay signal to retransmitters. Such manner of work
> means that we must time moments of interruption well. But we have a
> problem: signal that we have to deal with passes through several
> go-betweens where signal is being retransmitted/encoded/decoded. So we
> recieve signal delayed by 2 seconds. This delay is fixed and newer
> changes. While operating on signal we have to deal with this signal's
> own virtual delayed time and so all computers and wall clocks (which are
> in fact computers too) have to be always synchronized with the same
> virtual time.
> This is where we face unresolved trouble: I have read man pages but
> haven't understood if it is possible to make ntpd take into account this
> delay. So that clients could synchronize with 2 sec time shift. Is it
> possible to resolve our problem?
> With best regards,
> Alexey Ivanov

There is no way to do this without diving into the NTP code and
intercepting the relevant system clock functions like gettimeofday(),
adjtime, etc. and there may be other unexpected places you would need to
do this. Is there any reason why you cannot just state to start 2
seconds after a specific time? Asking NTP to do the offset for you seems
like a bit of overkill and will cause problems down the line if people
don't know about the special setting.


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