[ntp:questions] Re: NTP and Cron
Richard B. Gilbert
rgilbert88 at comcast.net
Wed Dec 1 03:02:08 UTC 2004
Steven Hajducko wrote:
>>ntp never decrements the time. If it's necessary it will reduce the
>>adjustments. Remember that time is monotonically increasing.
>>The only time you could get something like this happening is if
>>you were to use ntpdate to SET the time. It's another reason to
>Ok, good to know, but that's a little confusing to a ignorant neophite such
>as myself. :)
>I guess I'm not understanding how NTP actually adjusts time, which is
>probably something I should take upon myself to read about, but nonetheless,
>a quick, ignorant question. If a system clock is running too slow, then it
>simply adjusts the time to be a little bit faster than real time? Adding
>.001 ( or whatever number ) to every second until you make up that extra
>second? And if the system clock is running too fast, it makes that second
>count for less, in all sense of the word, slowing down the machine's time
>until real time catches up?
>Guess I should start my reading. :)
>Thanks for the info.
Yup! NTP fiddles with the clock frequency to make it run a little
faster until it catches up or a little slower until time catches up with
it. The current version of ntpd can be requested to set the clock on a
one time basis with the -g option. It will do so if the time is within
certain limits. You should set the clock manually to within a minute or
so of the correct time before starting ntpd. With older versions of
ntpd you would need to use ntpdate to set the clock before starting ntpd.
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