rtc net update

Colin Watson cjwatson at ubuntu.com
Mon Dec 11 11:26:32 UTC 2017

On Sun, Dec 10, 2017 at 08:03:50PM -0800, John R. Sowden wrote:
> Now that we are on the topic of the RTC, is it possible to change the update
> frequency.  I understand that a crystal controlled clock drifts a few
> seconds per month.  I also heard (unofficial) that routers, computers,
> tablets, phones, etc. do a net update daily.  Shouldn't a monthly update be
> enough, except for those few cases that more often is necessary?  Wouldn't
> this reduce the traffic on the net by, say, a lot?  Wouldn't that be a good
> thing?  I have never seen a prompt to vary the update frequency.

I'm not sure where the "daily" information comes from; at least ntpd
typically polls significantly more often than that, although it can be
configured; see ntp.conf(5).  If you're using ntpdate then you could
have a cron job to run it at whatever frequency you like, but it's
generally better to just run an NTP daemon instead for the reasons given
in ntpdate(8).  A decent NTP daemon won't just periodically slew the
clock, but will prefer to gradually adjust the clock frequency in a
feedback loop.

Regarding network traffic minimisation, NTP traffic is a drop in the
ocean, and it usually results in less surprising system behaviour to
make frequent small adjustments rather than infrequent larger ones.  I
would normally recommend leaving this sort of thing well alone.

Colin Watson                                       [cjwatson at ubuntu.com]

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