[ntp:questions] Increase maximum frequency offset to deal with really bad clock

Unruh unruh-spam at physics.ubc.ca
Mon Mar 9 23:09:16 UTC 2009


fwayne at frankwayne.com (Frank Wayne) writes:

>While several people suggested that Jeff use guest/host synchronization, no one ever answered the first question, "is it possible to override the maximum offset PPM?"

>-----Original Message-----
>From: questions-bounces+fwayne=frankwayne.com at lists.ntp.org [mailto:questions-bounces+fwayne=frankwayne.com at lists.ntp.org] On Behalf Of jeff at sailorfej.net
>Sent: Wednesday, 28 January 2009 14:46
>To: questions at lists.ntp.org
>Subject: Increase maximum frequency offset to deal with really bad clock

>Hi folks,

>I have a some FreeBSD systems running as guests in Microsoft Virtual
>Server.  There is a known problem with these were the clocks run very
>fast.  I am trying to use ntpd to keep their clocks in sync, but the
>frequency error offset is exceeding (I think) ntpd's maximum of 500,
>my driftfile always contains a value of "-500.000".  If understand the
>way this works correctly, if I could get the frequency error offset to
>represent the real error rate which I believe to be much higher that
>500 PPM, then ntpd would be able to keep the clocks in sync, as it is
>now, it slowly falls behind until it fails to correct altogether.

>So is it possible to override the maximum offset PPM in the driftfile,
>or is there a better way to fix this?


Recompile. ( Change include/ntp_proto.h 
#define SLEW    500e-6
to
#define SLEW    500e-5
for example to make it 10 times larger. Not sure if this will work or not. 

However, you should NOT be running ntp on a virtual system anyway. It makes
little sense since hardware cannot be vitualized. 





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