[ntp:questions] ntp & system without a rtc

Gabs Ricalde gsricalde at gmail.com
Fri May 10 19:17:53 UTC 2013

On Sat, May 11, 2013 at 2:48 AM, Richard B. Gilbert
<rgilbert88 at comcast.net> wrote:
> On 5/10/2013 10:36 AM, folkert wrote:
>> Hi,
>> I have a raspberry pi system. This is a computer without a real time
>> clock. So everytime I power it on, it uses starts where it left off
>> which might be days earlier. It is connected only very occasionally to
>> the internet so syncing to that won't work. It does have, however, a gps
>> connected. But as it is switched mostly for less than an hour, ntpd
>> won't have the time to adjust the time to what the gps returns to it.
>> So I was wondering: is there a utility/a trick out there that picks the
>> current time from a gps and then "jumps" the time to what it should be?
>> It does not need to be very accurate - a couple of seconds off is ok
>> (just not hours or days).
>> Any ideas?
>> Regards,
>> Folkert van Heusden
> I think you may be out of luck on this one.  If you can run NTPD 24x7
> you can have the correct time 24x7.  If you can't do this, NTPD is a poor
> choice.  The problem is that NTPD needs something like ten hours to select a
> time source and match the time!
> There is another "product" called "chrony" that has MUCH faster convergence.
> I't never used chrony and can't tell you much about it.
> I run 24x7 and seldom have to shut down and restart.

chrony's convergence is really fast: about a few minutes for a PPS
refclock. If you want to run ntpd after, copy the kernel's frequency
from ntptime into ntpd's drift file, kill chrony then start ntpd. No
need to wait for minutes/hours for ntpd to converge.

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