On Tue, 2008-11-25 at 09:25 +0100, Maarten Wiltink wrote: ... > [...] > > What's the best way to determine which of our NTP servers provides the > > best local clock? > > First order: reset drift (delete all their drift files), synchronise their > watches, let them run for a few days, and see which one has drifted least. > Correct for drift. > > This depends on how well you can put them all in the same starting state > by hand, and on the time source you use to measure drift at the end. You > can correct for the former by waiting longer. You _cannot_ outwit your > dependency on the latter. > > Second order: after the previous procedure, they should all drift very > little, and no one significantly more than any other. The one that stays > closest to that time source you're comparing against has 'the best local > clock'. This depends mostly on temperature stability.
So, to recap: ##>> Delete the NTP drift files. ##>> "Synchronizing" their clocks: 1. Stop NTP daemon 2. Consult http://wwp.greenwichmeantime.com/time-zone/usa/eastern-time/ 3. Construct a "date" command with the next minute after what's observed in step 2 and zero seconds. 4. Copy the date command and watch the count-up to the next minute on greenwichmeantime.com. 5. Paste the date command into the terminal window exactly when the counter turns to the next minute on greenwichmeantime.com. 6. Execute "hwclock --systohc" to set the hardware clock. 7. Start NTP daemon Repeat this for each NTP server ##>> Wait 4 days (Thanksgiving day weekend) ##>> Record value in NTP drift files Ex: [EMAIL PROTECTED] root]# cat /etc/ntp/drift 20.196 ##?? Is this a good source to measure the drift? ##>> Correct for the drift: ntptime -f 20.196 -or- adjtime -f (result of some formula) ##?? Not sure about the signage here. From what I've read, the value stored in the drift file is the frequency offset - the value required to bring the clock back to normal. ##?? Should this be done with ntpd stopped or running? From the man page it seems this command communicates with the running kernel. Is there a kernel parameter I can set in /etc/sysctl.conf to make this setting persist? The only thing I can see related to the clock in /proc is "/proc/sys/dev/rtc/max-user-freq". ##?? Is this what you had in mind? Thanks! ./Cal _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
