I don't understand how you get the idea that your system is
synchronizing with only one server when the messages you posted show it
synchronizing with 6 servers. Do you mean that it is synchronizing with
one server at a time? That is what it is supposed to do. There is a
combining step in the algorithms that can adjust the actual offset used
by combining with offsets from others in a selected group, but there is
always a single primary sync source.
On 8/14/2013 11:03 AM, Nils Brubaker wrote:
Thank you, un...@invalid.ca, for your response to my question.
Couple follow-up questions. My ntp.conf running on Linux has 4 servers
defined:
server 0.rhel.pool.ntp.org
server 1.rhel.pool.ntp.org
server 2.rhel.pool.ntp.org
These are public servers from the NTP pool project. In my
/var/log/diag-log file, I see messages indicating that my ntpd is synching
with individual servers, for example:
Aug 7 09:53:58 yellowstone ntpd[3272]: synchronized to 69.50.219.51,
stratum 2
Aug 7 10:04:52 yellowstone ntpd[3272]: synchronized to 184.82.112.110,
stratum 2
Aug 7 10:39:05 yellowstone ntpd[3272]: synchronized to 69.50.219.51,
stratum 2
Aug 7 11:28:17 yellowstone ntpd[3272]: synchronized to 184.82.112.110,
stratum 2
Aug 7 12:47:06 yellowstone ntpd[3272]: synchronized to 128.10.19.24,
stratum 1
...
Aug 8 11:37:43 yellowstone ntpd[3254]: synchronized to 50.116.55.65,
stratum 2
Aug 8 12:18:46 yellowstone ntpd[3254]: synchronized to 50.116.55.161,
stratum 2
Aug 8 13:01:27 yellowstone ntpd[3254]: synchronized to 38.101.77.21,
stratum 2
Aug 8 15:01:00 yellowstone ntpd[3254]: synchronized to 50.116.55.161,
stratum 2
Aug 8 16:09:20 yellowstone ntpd[3254]: synchronized to 38.101.77.21,
stratum 2
These log messages suggest that ntpd is synchronizing with one and only
one NTP server. Is that the correct interpretation? Is this single
server selected for synchronization only after performing all the
calculations described below?
Also, I see long time periods in the diag-log where there is no
synchronization message. What does that signify? No agreement between
the servers on the correct time? No need to adjust system clock because
it is already in sync?
Thanks,
Nils Brubaker
On 2013-08-13, Nils Brubaker <ncb at us.ibm.com> wrote:
For ntpd 4.2.4p6 running on Linux, is there any significance to the
order
of servers in the ntp.conf file? Will ntpd synchronize with the first
available/good time server in the list?
No, no.
ntp gets the data from all the servers. It then looks at the times it
gets from each server, and groups them into "classes" according to its
estimate of the max time error from the server-- ie whether the error
intervals overlap or not. It then looks for the largest group of servers
all of whose error intervals overlap and uses the average of those times
as the time to send on the the ntp engine. The others are "false
tickers". It estimates the error by looking at the round trip time and
the other machine's estimate of its own max error.
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