[ntp:questions] NTP vs chrony comparison (Was: oscillations in ntp clock synchronization)

Harlan Stenn stenn at ntp.org
Wed Jan 23 06:22:57 UTC 2008

>>> In article <4796CB87.7070400 at ntp.isc.org>, mayer at ntp.isc.org (Danny Mayer) writes:

Danny> Harlan Stenn wrote:
Unruh> Unfortunately I cannot run both ntp and chrony on the same system at
Unruh> the same time.
>>  Bill,
>> Exactly why can you not run ntpd and chrony on the same system at the
>> same time?

Danny> Harlan, really. You *cannot* have two different
Danny> mechanisms/applications to discipline the clock at the same time. I
Danny> invite you to try. You have access to my code so you can test this
Danny> easily.

You are, as is so often the case, missing my point.  It is possible to run
ntpd in a way that it does not discipline the clock.  I am curious about
your last sentence though - what is special about your code that would allow
this to be tested?

>> I want the ability to run multiple instances of ntpd where at most 1
>> instance of ntpd is actually controlling the clock, specifically to make
>> it easy to (more quickly) analyze the performance/behavior of different
>> configurations of ntpd.  I understand that the boat is rocking while this
>> is going on, but I suspect this capability would be a useful one in at
>> least some cases.

Danny> I don't see the benefit of doing this with two separate
Danny> instances. It's easier and simpler to just add the other servers into
Danny> the one instance and specify noselect.

Again you are missing my point.  Allowing this would let us, for example,
see how two different versions of ntpd would discipline the clock.  It would
allow us to see how ntpd might discipline the clock compared to chrony.

I understand and "get" that by not actually disciplining the clock we are
removing an important part of the feedback loop, and I do not know if that
will fatally affect these sort of experiments or not.

And as Bill said, it would be Swell if there was a way to do this using, eg,
virtual machines so that we could test them that way.  Better yet, it would
be nice to have a simulator framework where we could run these tests faster
than in real-time.
Harlan Stenn <stenn at ntp.org>
http://ntpforum.isc.org  - be a member!

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