[ntp:questions] Win7: ntpd adjusting time backwards

David Woolley david at ex.djwhome.demon.invalid
Sat Dec 8 21:03:55 UTC 2012

Jeroen Mostert wrote:

> I thought ntp could adjust the time forwards in "big" steps, but would 
> never adjust the time backwards. I'm guessing I got confused with the 
> slew-only option (-x) for servers that absolutely cannot tolerate the 
> clock going backwards, even if it takes forever to adjust it through 
> slew only.

Even -x doesn't disable steps, it just requires a larger error (600ms) 
before stepping.  Also note that increasing the error before stepping 
forces ntpd into a degraded mode where runs the discipline algorithm in 
user space, every second, and runs the clock at +/- 500ppm for a 
fraction of each second.  In the normal mode, on suitable systems, the 
kernel deals with the fine detail at the clock tick rate.

> With your explanation, I'm perfectly willing to blame crappy network 
> conditions and/or crappy pool servers on the frequent adjustments. 
> Looking at another machine, I see zero (0) adjustments there since ntpd 

If you suffer from temporary severe asymmetric delays, you can use the 
huff and puff tinker option to try and compensate.

> was configured to use a central, local time server (stratum 2). This 
> machine has no time-critical services, so as long as it's accurate to 
> within 1 sec/day I can't complain. I was just confused about the clock 
> going backwards.

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