[ntp:questions] stepping and slewing

Richard B. Gilbert rgilbert88 at comcast.net
Sun Apr 29 21:25:23 UTC 2007

Riccardo Castellani wrote:
> What is difference among stepping and slewing mode which are used by ntpd ?
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Slewing means that ntpd adjusts the clock at a maximum rate of 500 
microseconds per second.

Stepping means that the clock jumps abruptly from some incorrect time to 
some reasonable approximation of the correct time.  In normal operation 
ntpd will not step the clock; any error less than 128 milliseonds will 
be corrected by slewing the clock.  An error of more that 128 
milliseconds in considered an abnormal condition!

Since correcting large errors by slewing the clock could take days or 
weeks to complete stepping is used but, as mentioned above, this is not 

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