[ntp:questions] Speed of ntp convergence

Danny Mayer mayer at ntp.isc.org
Sun Dec 28 05:25:58 UTC 2008


Richard B. Gilbert wrote:
> Unruh wrote:
>> I should NOT have to check up on the drift file to see if it is correct.
>> That is the computer's job. ntp should NOT take 10 hours to correct a wrong
>> drift file. With a 16 sec poll, ntp should NOT have a 1 hour time constant.
> 
> Your opinion!  The designers/developers evidently disagree.

Not necessarily. The question that you need to ask is how do you *know*
that the drift file is correct? Remember that at boot time the system
has no concept of what the correct time is, never mind the frequency. If
the system has been powered down for a while, ie cold, the frequency
corrections may need to be different, but you have no way of knowing
this from within ntpd (or any other application). The drift file
contains data from the system at a steady state but on startup it's
hardily steady.

The question of correcting errors is a separate question but we
generally  recommend that people use the -g option to ntpd to ensure a
quick correction which allows an unbounded step of the clock. This will
not normally affect applications on the system if iburst is used for
external servers.

Danny




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