what was up with ntp again?
keybounce at gmail.com
Mon Mar 23 09:52:19 PDT 2015
> The longer version I'll briefly gloss: Apple replaced traditional ntp with one that uses less power and is more laptop friendly, when it works right. But it assumes that the clock drift of a brand new machine is the same as that of a fully burned-in and deployed machine, which it might well not be. The above commands are a "quick reset" of the clock drift, but as Apple removed some parts of ntp they may not be sufficient to determine the current clock drift; in that case, you need to use a full ntpd to characterize the drift, then switch back to Apple's for the improved performance and power management.
When I tried using the Apple NTP and pacemaker, what I discovered essentially is that NTP does NO clock adjustment at all. All the clock adjustment comes from pacemaker. Unfortunately, it did not do a good job of synchronizing for me. In particular, the Apple NTP was never able to get past a poll of 256, and almost always was at 64. The drift file wanted to be over 500 no matter what I did with the stock config.
For a good approximation, what I do is get a "real" ntp, and run it until it knows what the drift should be. Then, I give that drift to pacemaker, and restart "real" ntp. This gives me a drift that is almost zero, and a very large ntp poll factor. I repeat this until the real ntp has almost zero drift over 2 days.
At this point, all the clock adjustment is from pacemaker. An ntpdate every few hours from cron, and pacemaker, will give you good time keeping and low power consumption.
But to do this, one of the two (pacemaker, or ntp) needs to be given a different drift file (they default to the same file, but are essentially using it for different purposes).
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