Re: ntp client over satellite and no CMOS battery

GNWIII@xxxxxxxxx wrote:

Brad Knowles wrote:



Note that ntpd can continue to run indefinitely, even though it
has not yet been able to get a sync. It will continue to try to get
a sync and then keep you in sync, until you reboot the machine.



Or the network goes down!

I have a similar situation to that of the original post.  The problem
with letting ntpd run is that you have to manually check between the
time that the network comes up when ntp is sync'd.  In my if-up.local I
have a "service ntpd restart", which (on fedora core 4) does ntpdate to
get the initial setting, then starts ntpd.  This way, the network
doesn't "come up" until ntpd has a good chance to sync.  I just leave
ntpd running after the network goes down.

More work needs to be done for sites with intermittent network access.
What is the cheapest way to keep ntpd sync'd to 10 s, 1 s, or 0.1 s
without network?



Most any GPS receiver should hold you within 1 millisecond or better and usually much better. A receiver designed for timing rather than navigation should give you time correct to +/- 50 nanoseconds; the limitation will be how closely your computer hardware and software can hold synchronization. Some hardware and software can do this very well indeed. Others; e.g. Windows and Linux do not do nearly so well.

You must be able to site an antenna with an unobstructed view of the sky in order to have continuous and reliable GPS signals. I have an old Sun Ultra 10 running Solaris 8 and ndtp 4.2.0 with a Motorola Oncore M12+T receiver. Ntpd claims to be synched to within eight microseconds; I'm inclined to believe it.
.

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