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

Nicola Berndt nb at komeda-berlin.de
Mon Aug 25 09:03:26 UTC 2008


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!



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