[ntp:questions] Getting NTP to correct only the clock skew

Steve Kostecke kostecke at ntp.isc.org
Sat Mar 31 14:42:53 UTC 2007

On 2007-03-31, Spoon <root at localhost> wrote:
> Steve Kostecke wrote:
>> Provide your ntpd with a stable PPS source and use the Undisciplined
>> Local Clock.
> I am running Linux
> I don't think vanilla 2.6 supports PPS sources at the moment?

You could bring up a system running a Linux kernel version with PPSkit
support. Or you could bring up a FreeBSD system. 

> In my situation, I don't care what time it is, but my clock needs
> to tick at the correct rate.

The least expensive means of getting your clock to tick at the correct
rate is to synchronize it to the ubiquitous time-base known as UTC.

> I think I can't use GPS because the computer is located in a server
> room underground.

Can you run an antenna cable down to the bunker? That would allow you so
place an antenna top-side and the GPS receiver underground:




If you can receive CDMA cellphone signals in the bunker you could use a
product such as the Endrun Technologies PraecisCT:


> Are there other PPS sources? I've read about rubidium and cesium clock 
> sources. How expensive are they?

Here's one rubidium oscillator (you'd have to package it into a complete
solution): Sanford Research PRS10 $1495 US / $1695 international

Here are some links for complete solutions (you have to request prices):



You should be able to find more using your favorite search engine.

Steve Kostecke <kostecke at ntp.isc.org>
NTP Public Services Project - http://ntp.isc.org/

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