[ntp:questions] Quick sync between two computers not connected to the internet

unruh unruh at wormhole.physics.ubc.ca
Wed Mar 24 20:35:19 UTC 2010


On 2010-03-24, Hal Murray <hal-usenet at ip-64-139-1-69.sjc.megapath.net> wrote:
> In article <0f5de21d-2a20-40fa-ab68-a03cba5ae90b at u9g2000yqb.googlegroups.com>,
>  Evandro Menezes <evandro at mailinator.com> writes:
>>On Mar 23, 11:38=A0am, Chuck Swiger <cswi... at mac.com> wrote:
>>>
>>> If I really had to solve the latter problem, I would likely connect the m=
>>achines to a valid NTP timesource long enough to calibrate each machines' i=
>>ntrinsic drift from realtime, and then run time in standalone mode against =
>>their local clock.
>>
>>Useless.  Clocks may drift wildly due to temperature changes, be it
>>ambient or inside the box.



>
> The temperature drifts that I've seen are much smaller than the
> basic calibration.
>
> On the other hand recent Linux kernels have screwed up the basic
> calibration on startup so rebooting a machine is much worse than
> a temperature change.  (If they have fixed it recently, I haven't
> seen any announcement.  You can fix it by hacking a constant into
> your kernel.)
Yes, it seems to be fixed. My machines with the more recent kernels are
getting about 10PPM out, while the older ones with the calibration
problems are more like 100-200PPM out.
and varying by 50PPM or so between boots. 
>




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