[Nottingham] "ntpq -p" displayed flags

Martin martin at ml1.co.uk
Thu Jan 26 14:26:12 UTC 2012

On 25/01/12 12:48, Chris Booth wrote:
> Hi Martin,
> Couple of links you could add:
> /usr/share/docs/ntp-4.2*/debug.html  
> http://www.ietf.org/rfc/rfc1305.txt  or the pdf at: http://www.rfc-editor.org/rfc/rfc1305.pdf
> The meanings (that you have already gathered together on your web page) of  ntpd -p's output are explicitly explained in:  /usr/share/docs/ntp-4.2*/debug.html  from where I get this quote: "The mean millisecond time offset (phase) and deviation (jitter) monitor the clock quality".  So *I guess* that means that the jitter number printed is a value indicating a range to indicate the accuracy of the phase value. 
> http://www.ietf.org/rfc/rfc1305.txt  has more details on how NTP is to handle the random noise (jitter) of hardware clocks, or fluctuations (jitter) in the network.  It also has an interesting explication of the changes in and relations between our timekeeping systems over the past 5,000 years or so - worth a quick read.
> .PTB. are the German timekeepers.
> .DCFa. is from an NTP radio receiver.

Thanks for that.

I ain't got no /usr/share/doc/ntp-4.2*/debug.html (nor docs)... But then
again I'm running a Gentoo system with the "-doc" 'use flag' (no docs)
for when it was a diskless system (ok, so it's now got an SSD a few
years later...) ...

Some further ferkling around and... Unfortunately there's various
variants on the man pages for ntpq, and Gentoo even has two versions...
Looks like a bug report is needed for that one from the confusion caused...

So, my version of a helpful page for ntpq stands at:

“ntpq -p” output

There's a LOT of interesting stuff behind all that lot! Some spectacular
long running work throughout the evolving ages of the internet.

What I have run out of time with is... How do you know what accuracy you
are running with? What timing error can be expected from what ntpq can
tell you? (Simply :-) )

Hope of interest,



Martin Lomas
martin at ml1.co.uk

More information about the Nottingham mailing list