[ntp:questions] time to sync vs ptp?

unruh unruh at invalid.ca
Fri May 31 15:31:39 UTC 2013


On 2013-05-31, matthew.garman at gmail.com <matthew.garman at gmail.com> wrote:
> On Thursday, May 30, 2013 2:21:15 PM UTC-5, Rob wrote:
>> > I have a server running NTP 4.2.2 (as part of the RedHat 5.7 release).  Last night I changed it's /etc/ntp.conf file, specifically the "server xyz" line to point to a new NTP server.
>> 
>> > After doing this, the clock's offset was *increasing* after an hour.  Offset is measured by "ntpdate -q peer".
>> 
>> 
>> This is a wellknown problem.
>> 
>> When you do a couple of ntpd shutdown/restarts e.g. because you
>> 
>> a experimenting with different server configurations, the combination
>> 
>> of ntpd and the kernel goes haywire and it will actually steer the time
>> 
>> the wrong way.
>> 
>> 
>> 
>> Just wait a day or so, and it will have solved itself.
>
>
> Would it be possible to provide a link or point me to some reference material where I can read more about this issue?

See the end of www.theory.physics.ubc.ca/chrony/chrony.html where I
discuss chrony vs ntpd

The idea is simply. If the rate is out, but the offset is small, then it
will take a while for that rate error to manifest itself in the offset (
which is the only thing used to drive ntp).



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