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

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Sat Mar 31 19:56:08 UTC 2007

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

How accurate do you need it?

You can get "pretty close" if you figure out what the drift
should be and use that.

You can get that two ways.

One is to let ntpd run while connected to the outside world.
It will leave the answer in log files and /var/ntp/drift or

The other is to do it by hand.  Start your system with no ntpd.
Compare it's time with a known good clock.  Wait a day/week/whatever.
Compare the clock again.  Now compute the drift.

If you can measure time within 1 second, you will have to wait
~2 weeks to get within 1 ppm.  The drift on some of my boxes is
~100 ppm, so that would correct most of the error.

Note that temperature has a significant influence on drift.
Your correction factor may change over the seasons or as
you rearrange things in your machine room.

You may get the wrong answer if you "connect to the outside
world" by moving the system to another location with a different

These are my opinions, not necessarily my employer's.  I hate spam.

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