[ntp:questions] On NTP server, how to check offset between client and NTP server?

David Woolley david at ex.djwhome.demon.co.uk.invalid
Fri Oct 10 07:52:29 UTC 2008

chowalit.lab Chowalit Lab Linux wrote:

>    -  My clients are windows XP, Windows 2003, Linux.
>       My question:
>    -  How to check the different time between NTP server and client on
> NTP server side.

That will be very difficult for the Windows ones.  For the Linux ones, 
add code to the clock interrupt routine that pulses a printer port line 
or modem control signal (do not use USB ports), and simultaneously 
writes the offset between the software clock time and the nominal, round 
number of milliseconds, tick time, to a buffer.  At user level copy that 
buffer to a file.

Do this on both client and server.

Set up some suitable instrumentation to measure and log the time delay 
between the pulses on client and server, then process the results in 
conjunction with the client and server's idea of the time at the time of 
the pulse.

This assumes that the machines are electrically close.

Don't worry too much on Windows, as the time is likely to be more 
accurate than the resolution with which ordinary application programs 
can read it.  If you are using w32time on XP, don't worry, because 
w32time is not intended for precision time keeping on that platform, and 
doesn't default for it on 2003.

If you want to measure the value during the startup and other transients 
that Dave Mills considers unimportant, use ntpq on the server.  This 
will not work for any machines using w32time.  You might also configure 
the client as an ignored server for the server, or maybe peering them, 
to allow ntpq peers run on the server, against the server, to give a 
reverse "offset" value.  Note these methods only give you historical 
information.  For a near instantaneous snapshot, use ntpdate -d.

The reason you are getting such complex answers is that you are asking 
to measure something that, in an ideal system, is theoretically 

More information about the questions mailing list