[ntp:questions] ntpd questions - FreeBSD 5.5

Danny Mayer mayer at ntp.org
Mon Jul 20 12:21:33 UTC 2009

David Shoulders wrote:
> Danny -
> I don't have a critical need for accuracy, so I didn't want to add any
> more load to the servers than necessary.  I thought that a few hits 4
> times a day would be a smaller load than running the daemon all the
> time.  Now that my computer's clock seems to be running inconsistently,
> the load from the ntpd running continuously would be even higher, right?

You won't notice any load running ntpd, it is almost invisible. I have
run ntpd and targeted 200 simultaneous clients at it for a load test and
it was like it was not not running. A server sends out a packet at most
once every 64 seconds (these are using default settings) per server
specified in the configuration file and usually much less frequently if
it has been running for a while.

> BTW, new data on my little mystery:  the computer clock seems to gain
> time (like 2 seconds in 3 hours) during times when I'm using my other
> systems -- never when idling.  This even though the computer is just
> providing nfs service and occasional backups.  Shouldn't an increase in
> average load slow the clock (by masking more interrupts)?

It sounds like the clock needs to be disciplined and by not running ntpd
continuously the clock is drifting too much. The question of the affect
of load on the clock depends on how it handles interrupts. Linux has had
that problem for years of losing interrupts while FreeBSD never has a

Run ntpd continuously and see if that solves your problem.


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