[ntp:questions] reading loopstats file, converting day and time

Mike K Smith mks-usenet at dsl.pipex.com
Fri Jan 23 15:12:56 UTC 2009


On 23 Jan, 03:18, anna_chen... at yahoo.com wrote:
> Hi, I need some help in interpreting the loopstats file, hope someone
> can help
> I have ntp configured so that it is generating the loopstats file, the
> file format is the following
>
> 54854 852.338 0.000779917 -85.871689 0.001363577 15.650605 10
> 54854 2390.510 -0.000000876 -85.871689 0.000993395 13.553822 10
>
> checking the linkhttp://www.ntp.org/ntpfaq/NTP-s-trouble.htm
> the entries represent
>
> day, second, offset, drift compensation, estimated error, stability,
> polling interval

I hadn't looked at that perticular webpage until I saw your post, but
there is more information on David Mills's website at
http://www.eecis.udel.edu/~mills/ntp/html/monopt.html

The page includes a table listing the fields in the loopstats file and
I think the descriptions of the fields are more helpful in that table.

----
loopstats
Record clock discipline loop statistics. Each system clock update
appends one line to the loopstats file set:

50935 75440.031 0.000006019 13.778 0.000351733 0.013380 6


	Item	Units	Description
             50935	MJD	date
       75440.031	s	Time past midnight
   0.000006019	s	Clock offset
            13.778	PPM	Frequency offset
   0.000351733	s	RMS jitter
        0.013380	PPM	RMS wander
                    6	log2(s)	Clock discipline loop time constant

----
[Crossing my fingers and hoping that Google Groups preserves the
spacing above.]

> I assumed the offset is the same offset as in ntpq -p in millisecond
> and the drift compensation is the same output as drift file for clock
> frequency error, but what are estimated error, stability and polling
> interval ? What are the unit of measurement? which output will be
> useful for monitoring potential problems?

The Jitter (estimated error) is defined in the draft RFC for NTP  as
the root-mean-square (RMS) average of the most recent offset
differences, represents the nominal error in estimating the offset.

The Wander (stability) is described as the RMS of exponentially
weighted frequency differences, so it is a measure of variation in the
drift.

Bill Unruh already explained the polling interval metric to you.

What tool are you using to analyse and graph the loopstats?

Mike




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