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

Unruh unruh-spam at physics.ubc.ca
Mon Aug 25 01:11:34 UTC 2008

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

Also as stated use the -g flag to ntpd

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