[ntp:questions] Re: how to read and understand ntpq -pcrv output - pre-wiki

Anthony DeRobertis netnews at derobert.net
Tue May 16 02:49:35 UTC 2006


On Mon, 15 May 2006 18:42:29 +0000, Jim Cromie wrote:
 
> ? refid - Ive seen other listings with different stuff here,
>     PGOA ?
>     PPS - pulse per second - usually off an atomic source, maybe GPS they
>     mostly look like IPs,
>     are they some kind of hierarchy id, ie hash on path of clock-refs /
> system peers?

Your system's primary peer (forget the right term), the one marked with a
* in the peers output, is what other people will see in the refid field.
The refid is "where did that machine get its time from?"

Not sure what PG0A is. But you'll often see things like PPS (any generic
pulse-per-second source); GPS, CDMA, etc.

Here is a peers output showing more examples of them:

anthony at feynman:~$ ntpq -c peers ntp.derobert.net 
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*GPS_ONCORE(0)   .GPS.            0 l    1   16  377    0.000   -0.003   0.015
+ntp2.usno.navy. .USNO.           1 u   69  256  377   13.399   -0.589   5.247
-navobs1.gatech. .USNO.           1 u  158  256  377   32.259    1.899   4.546
+bonehed.lcs.mit .CDMA.           1 u   32  256  377   24.350   -0.015  12.079
-time-b.nist.gov .ACTS.           1 u   52  256  377   10.486   -5.637   3.223


> 
> ? delay, offset, jitter are in  milliseconds ?  (if rtfm, I havent seen
> it, pointers welcome)

yes.


> good values are _______

as low as possible :-D

The maximum amount your clock can be off (assuming the peer's clock is
right) is 1/2 of the delay. 

Offset how much your clock is off, according to the most recent response
from that peer. 

Jitter is, I think, how much offset is jumping around from packet to
packet.

[Sorry for ignoring the rest of the questions. I'm not quite sure what
rootdispersion, etc. is. I think you're right about frequency, though]




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