[ntp:questions] Re: ntpd, boot time, and hot plugging

Per Hedeland per at hedeland.org
Sun Feb 6 16:22:05 UTC 2005

In article <ZLidneYGhOB1uZvfRVn-pA at comcast.com> "Richard B. Gilbert"
<rgilbert88 at comcast.net> writes:
>Per Hedeland wrote:
>>In article <vaKdnSNBMfU2upnfRVn-uQ at comcast.com> "Richard B. Gilbert"
>><rgilbert88 at comcast.net> writes:
>>>The user may wish to specify the required accuracy, knowing that there 
>>>is a trade off with elapsed time to achieve that accuracy.  How good 
>>>"good enough" must be will vary.   Someone recording the time workers 
>>>started work and the time they stopped may be satisfied with plus/minus 
>>>one minute but it's 8:00AM local time and he needs it right now!  
>>>Someone else might really need plus/minus ten microseconds and be 
>>>willing and able to wait two or three hours to get it.
>>This I think is way beyond "what people are looking for" in this
>>particular area - and I'm not sure it's very meaningful either: It makes
>>no sense to set the time with great accuracy and then just leave it,
>>since the clock will quickly drift away. Achieving and *maintaining*
>>great accuracy, by calculating and taking the drift into account, is
>>precisely what ntpd already does in its normal mode of operation, of
>I'm not suggesting that ntpd should set the clock and let it drift!  
>Having once set the clock, ntpd would resume normal operation with "good 
>enough" values of time and frequency.  An additional minute or two would 
>be required to check the clock frequency.  If it takes two minutes and 
>the frequency error is less than 500ppm, as it must be if ntpd is to 
>work at all, the clock could not drift more than sixty milliseconds in 
>two minutes.

OK, I probably got confused by the "The user may wish to specify the
required accuracy" part - this made me think that you were talking about
a separate program (or possibly ntpd in "-q mode"), that would exit when
the required accuracy had been achieved. In the context of a special
startup mode for ntpd, with ntpd resuming normal operation before that
accuracy was achieved, I'm not sure I understand where this "required
accuracy" would fit in... - should ntpd somehow signal the environment
at the point when it was achieved?

--Per Hedeland
per at hedeland.org

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