On 3/13/2012 6:42 PM, Chuck Swiger wrote:
On Mar 13, 2012, at 3:19 PM, Ron Frazier (NTP) wrote:
At that time, I had the GPS as the only selectable clock, for testing. I'm
monitoring the internet servers for comparison. I've since selected 1 NIST
server as the preferred and only selectable clock, and am monitoring the GPS
and other internet clocks for comparison.
ntpd is probably better able to judge which timeserver to use then forcing the
choice via prefer, as it continues to evaluate the servers available to it and
will use another one if the chosen peer happens to become unreachable.
My thinking was simply that if all the available clocks vanished (internet
down), or the GPS went insane, I just want the system to coast on its internal
clock until a viable clock source returns. I figure it may gain or lose up to
10 ms / minute this way, but at least it shouldn't do anything radical like
jumping 50 seconds.
If you let ntpd run long enough to estimate the intrinsic drift, it will
continue to adjust the clock even without external timesources. However, if
your system clock really is off by a rate of 1:600 or worse, it's broken and
ntpd probably wouldn't be able to fix it, at least without tinkering the max
allowable slew rate-- running ntpdate via cron might do.
I looked at the docs page for the "orphan" command for a few minutes and my
eyes just glazed over. I decided to try the local clock option instead for now.
Why would you want to use the local clock option? It's rarely the right
solution, barring unusual circumstances...
Regards,
I was speculating that perhaps my only selectable clock, the GPS,
failed, and that something went nuts, and that's why I found the clock
50 seconds off this morning. However, I don't have any evidence of a
GPS failure. In any case, I just figured the local option might prevent
any major clock changes if all other sources are not available. I only
wanted the local option to kick in if there were no other sources. I
did not have that option in the ntp.conf file when I started this
thread. When I started this thread, my GPS was the only selectable
clock, and there was no local option.
For now, I'm mainly wanting to compare the GPS to one primary other
source because I've been experiencing a slow drift in NMEA time with a
variation of about 120 ms and an oscillation period of several days.
I'm trying to isolate the source, either the GPS, or the subsystem
that's getting time from the internet servers. I'm assuming all the
internet servers are not drifting, but my instrumentation, ie the
Meinberg time server monitor, or whatever drives it, could be off.
That's why only have one source selectable, either the GPS, or one NIST
server.
Sincerely,
Ron
--
(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
such. I don't always see new messages very quickly. If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)
Ron Frazier
timekeepingdude AT c3energy.com
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