[ntp:questions] Re: HowTo calibrate system clock frequency using NTP
David L. Mills
mills at udel.edu
Mon Feb 6 22:15:39 UTC 2006
Daniel,
The peer offset is recorded for each client/server exchange. Let it run
for a few hours and record the time of day and the offsets at the
beginning and end. Subtract and divide by the interval. It's really not
complicated.
Dave
Daniel Kabs wrote:
> Good afternoon David,
>
> I think we are talking at cross-purposes: in case of Plan B, you
> suggested to use the option "disable ntp" (so there should be no
> frequency correction) and to read the time offset at intervals using
> ntpq -c 'rv <assoc_id_of_peer>'
>
> If I configure ntp that way, this is how the billboard looks on my
> system after some days of running time:
>
> # ntpq -c 'rv 16532'
> status=9634 reach, conf, sel_sys.peer, 3 events, event_reach,
> srcadr=10.0.0.254, srcport=123, dstadr=0.0.0.0, dstport=123, keyid=0,
> stratum=1, precision=-18, rootdelay=0.000, rootdispersion=6.989,
> refid=DCFa, reftime=c7919b26.416249a1 Mon, Feb 6 2006 10:53:42.255,
> delay=0.688, offset=-114389.792, jitter=75.264, dispersion=0.947,
> reach=377, valid=7, hmode=3, pmode=4, hpoll=6, ppoll=6, leap=00,
> flash=00 ok, org=c7919b4f.ed9e6256 Mon, Feb 6 2006 10:54:23.928,
> rec=c7919bc2.517e5647 Mon, Feb 6 2006 10:56:18.318,
> xmt=c7919bc2.514cec41 Mon, Feb 6 2006 10:56:18.317,
> filtdelay= 0.69 0.68 0.77 0.79 0.88 0.77 0.69 0.69,
> filtoffset= -114389 -114372 -114353 -114335 -114316 -114299 -114282
> -114264,
> filtdisp= 0.01 0.97 1.96 2.92 3.91 4.87 5.83 6.82
>
>
> I was asking about reading the "offset" variable:
> offset=-114389.792
> What is the corresponding time when this variable was set? The
> billboard show several candidates ("reftime", "org", "rec" or "xmt"),
> but I don't know which one is the correct one.
>
>
> Cheers
> Daniel
>
>
> David L. Mills wrote:
>
>> Daniel,
>>
>> Your question does not parse. The frequency correction has nothing to
>> do with the state variables you quote. The time the frequency
>> correction is monitored is prominently displayed on the ntpq rv
>> billboard.
>>
>> Dave
More information about the questions
mailing list