Re: [chrony-users] High skew values

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On Wed, 24 Jul 2013, Arnon Weinberg wrote:

On 2013-07-24 09:17, Bill Unruh wrote:
 Are you running chrony on a virtual machine?

Indeed (a "cloud" server).  Any suggestions?  I'm having a hard time finding

The problem is that such virtual servers do not keep good time. The idea is to
keep the underlying OS (the one that is running the virtual server) on time
with something like ntp or chrony, and than have the virtual server get its
time from that underlying system. It is clear that your system's time is changing rapidly and unevenly (ie the
rate changes rapidly). In that case using more than one server is
counterproductive. Thus, I would try to run chrony with one server, not 4
(yes, I know that 4 is the recommended minimum but that is for a normal
machine). Chrony will then try (probably not terribly successfully) to follow
that one machine. I would also up the polling interval to a maximum of 6 and 4
if you canget away with it. You really then have to get permission from the
people running that server, since that rapid a poll interval is usually
considered abuse.

any documentation on best practices for running chrony on a virtual machine, although documentation seems to indicate that this is quite normal to do:

I am not quite sure what Miroslav means by the sentence
"larger range for frequency correction (100000 ppm vs 500 ppm), useful for
systems running in virtual machines which may have quickly drifting clocks"
well I do now what he means bu the first half, but am not at all sure how
useful the second half is, since not only will it have a high drift rate but
also a high fluctuation in the drift rate.

 the various sources disagree by 22 sec

That's not so bad compared with several hours of accumulated drift over a day or so. I'll happily live with +/- 1 minute errors if chrony can be adjusted to accept that.

William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
Physics&Astronomy  |     Advanced Research  |     Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology |     unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1     |      and Gravity       |

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