[ntp:questions] Very large offset and jitter values after reboot

Unruh unruh-spam at physics.ubc.ca
Mon Aug 25 17:57:44 UTC 2008

nb at komeda-berlin.de (Nicola Berndt) writes:

>Unruh schrieb:
>> nb at komeda-berlin.de (Nicola Berndt) writes:
>>> Richard B. Gilbert schrieb:
>>>> Nicola Berndt wrote:
>>>>> Hello,
>>>>> I have now successfully set up my machine to use a usb-gpd-mouse to set 
>>>>> the time. Strangely every time I reboot I get results like this, wich 
>>>>> settle down after a (not so short) while:
>>>>>      remote           refid      st t when poll reach   delay   offset  
>>>>> jitter
>>>>> ==============================================================================
>>>>>  GPS_NMEA(0)     .GPS.            0 l    9   64   37    0.000  -580.75 
>>>>> 3965.19
>>>>> The problem is, that this takes rather long and the computer's job 
>>>>> actually is, to provide exact time outdoors right after booting..
>>>>> I already tried what would happen if I did a 'hwclock --systohc' once 
>>>>> things are settled, but with no luck. My driftfile btw. says -35.666 - 
>>>>> looks good to me - and I am very worried about the huge jitter...
>>>>> Any ideas for me, anyone?
>>>>> Thx and regards,
>>>>> ../nico berndt
>>>> 1.  Don't reboot!  My Windows, Linux, Solaris, and OpenVMS systems will 
>>>> all run until the power goes off for longer than the run time of my UPS.
>>>> 2.  Start ntpd with the "-g" switch.  The -g switch tells it to get and 
>>>> set the correct time.  Following startup, ntpd will discipline the clock 
>>>> in the usual way.  It may take a relatively long time, around thirty 
>>>> minutes, to settle into really tight synchronization.
>>>> _______________________________________________
>>> 1, As I wrote already, the device has to work outdoors, where there is 
>>> no unlimited power-source, so I have to reboot. Also I think, a computer 
>>> that cannorttake a reboot has a problem wich needs to be adressed. Just 
>>> my opinion, though..
>>> 2, I forgot to mention that I already do so, still takes too long to 
>>> settle. I also don't understand what is taking so long, since - jitter 
>>> or not - the nmea time is precise enough to just quickly set the time at 
>>> startup and then let things go their way. Can someone explain that to me?
>> You could try chrony ( assuming you are on Linux) which has the ability to
>> handle the rtc as well and correct for its errors. It settles down much
>> faster than does ntp, and gives tighter control over the clock in many
>> situations. 
>Don't know chrony yet, I'll look into it. Thx!

Sorry-- don't bother. chrony does not support hardware clocks ( like your
nmea clock)
It would be really nice if someone installed glue into chrony so it could
use the ntpd hardware drivers. I do not have the time or competence.

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