I am facing an issue of large offset coming from my GPS clock.
I am syncing RHEL 6.3 server by GPS clock through ntpd service. I have too servers of same type and both are syncing independently to the GPS Clock.
>ntpstat of server 1 gives,
Code:
Synchronised to unspecified at stratum 15
time correct to within 145 ms.
Synchronised to unspecified at stratum 15
time correct to within 165 ms.
>ntpstat of server 2 gives,
Code:
Unsynchronised
polling server every 16 s
I also found that there is a difference of 50 seconds between Linux system clock and GPS time in server 1 and 2.
I have run ntpdate -d (GPS Clock IP) and stop the NTPD service.
Run,
>hwclock -S in RHEL system and restarted NTPD service hoping that it will decrease the time between source and synch and NTPD will be able to adjust the time now.But unfortunately offset and jitter in increasing and RHEL servers' time lag increases w.r.t time.
I am finding difficult to understand the above happenings.Can somebody suggest how to troubleshoot the issue?
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Last edited by Don Cragun; 04-21-2017 at 06:48 PM..
Reason: Add CODE and ICODE tags.
You should always try to use at least three sources for NTP. The NTP daemon running on your system will throw away the time that has the highest drift and then average the remaining times to set the local system time. This will eliminate any one source that has drifted and reduce the risk of a slow network response.
In short, try using three sources and see if that fixes your problem.
It looks like there is something wrong with the time that is being served by server2 and it's configuration. This would be solved by having 3 credible sources.
If ntpq -p shows high and growing offsets, then usually it means that the clock control in the kernel does not work.
So it looks that both server1 and server2 are suffering.
But I wonder why ntpstat on server1 looks okay.?
Are server1 and server2 virtual? I have seen this on VMware ESX guests: the clock steppers are ignored, and the clock needs to be set on the VMware ESX host.
After a lot of brainstorming and consulting with some NTP expert I found the following.
Code:
2 May 17:00:28 ntpd[2178]: synchronized to 172.31.64.10, stratum 1
2 May 17:36:39 ntpd[2178]: time reset -0.313640 s
2 May 17:37:13 ntpd[2178]: synchronized to 172.31.64.10, stratum 1
2 May 17:52:12 ntpd[2178]: time reset +0.491725 s
2 May 17:52:31 ntpd[2178]: synchronized to 172.31.64.10, stratum 1
2 May 18:08:34 ntpd[2178]: time reset +0.283749 s
2 May 18:09:49 ntpd[2178]: synchronized to 172.31.64.10, stratum 1
2 May 18:50:31 ntpd[2178]: time reset -0.312960 s
2 May 18:51:34 ntpd[2178]: synchronized to 172.31.64.10, stratum 1
2 May 19:06:30 ntpd[2178]: time reset +0.481487 s
NTP expert comment:
Code:
This means whenever the system time is synchronized, a few minutes late
the time offset is again so large (> 128 ms) that ntpd is unable to
correct it smoothly. So it steps the system time ("time reset") and
restarts from scratch.
So this looks like the timekeeping in your Linux system is broken, i.e.
the system time increases not continuously at the same rate.
NTP is unable to fix some broken timekeeping. Only if the timekeeping is
stable, NTP can determine the current offset, the time drift, and adjust
the system time smoothly so that the time offset is continuously as
small as possible.
I don't thing there's a problem with the package exchange. It's just the
Linux system time which has too much jitter, i.e. changes quickly from
increasing too faster to increasing too slow. You need to fix that
first, otherwise you are out of luck.
Now the question is How to fix the "BROKEN TIMEKEEPING OF LINUX System"?
Can some body help me out?
Last edited by Corona688; 05-08-2017 at 12:38 PM..
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04-21-2017
