[ntp:questions] ntpd on dial up machine: no DNS resolving => giving up on all servers

David Woolley david at ex.djwhome.demon.co.uk.invalid
Sun Jun 7 09:26:33 UTC 2009


Richard B. Gilbert wrote:

> 
> Whether or not ntpd steps the clock depends on how far off it is.  If 
> the clock was off by 15 minutes, most people would want it corrected 
> immediately rather than having the offset amortized over three or four 

More like three or four weeks, if the clock frequency error is << 500ppm.

> days!  I believe that the default threshold is 128 seconds; less than 
> that, the clock will slew.  If more than 128 seconds the clock will step.

The threshold is 128ms.  Anything more than 0.5seconds disables the, 
higher accuracy, kernel discipline.

Note, if one doesn't mind backwards steps of less than many seconds, one 
would need ntpd offline for many days to have problems.
> 
> If exact time and/or close agreement among a number of systems is 
> wanted, it's best to try to keep the systems up 24x7; the reason being 
> that NTPD may need as long as ten hours to synchronize the clock from a 
> cold start.  Once synchronization has been achieved, NTPD should be able 
> to maintain it with little effort.  Keeping the systems running also 
> tends to stabilize the temperature which can be most helpful in keeping 
> accurate time.

I believe the issue is keeping the internet connection running, rather 
than keeping the machine running.




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