On Wed, 2008-11-26 at 00:52 +0000, Unruh wrote: [...] > >Okay, so I'll just be using the difference in seconds between one > >invocation of "date" and the next. > > >How do I translate these seconds into a usable value for "ntptime -f"? > > 1sec/day=11.47 PPM. scale for other values. > (Ie, convert the time difference to seconds per day, and multiply by 11.5) > If the computer time is fast you need to slow down the computer clock. [...] > >> >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 > >> > >> No way you will get that kind of accuracy using this procedure. > >> You will be lucky with a few PPM > > >I wasn't aware that I had illustrated any level of accuracy. As I said, > >I'm shooting for about 1 sec per day. > > 20.196 is a number which seems to be accurate to .001 PPM.:-)
Oh, I see what you're saying. All I did was to pull the number from /etc/ntp/drift (ntpd's drift file) and paste it into the ntptime command. Doesn't the "-f" argument specify frequency offset and the drift file contains the frequency offset calculated to that point? > >I'll look at "chrony" but I want whatever NTP implementation we use to > >be as maintenance free as possible once it's in operation. I don't want > >someone to have to manually update anything every day or week. > > Well, that daily or weekly input of the time is to keep your system on > time. It will drift. And if you want to correct that drift youhave to give > it more data. 1 minute every couple of months would be fine. > >That's what I'm asking. Is there a kernel parameter to set frequency > >offset? If not, how do I make the calculated offset persist across > >reboots? Aside from a kernel parameter entry in /etc/sysctl.conf the > >only way I can think of is to add the full comand "ntptime -f (offset in > >PPM)" to "/etc/rc.local" or "/etc/rc.sysinit". > > You could do that. > > Note that the recent linux kernels have apparently totally messed up the tsc > hardware > clock. The drift rate changes by 50PPM between successive reboots, so you > old drift file is useless on the new boot. You need to make sure that the > machine use the acpi_pm (?) or hpet as their timing source, not the tsc. Thanks for that info I'll keep that in mind. Well, in my notes anyway. :-) ./Cal _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions