On 2011-08-27, Chris Albertson <albertson.ch...@gmail.com> wrote: > On Sat, Aug 27, 2011 at 9:49 AM, C BlacK <rb...@non.net> wrote: > >> I read somewhere that it takes an ntpd 24 hours to truly sync up to a >> stratum 2 master. >> >> > Use some logic. Assume you want to set a mechanical clock's speed by > moving the "slow/fast" lever and you can see the time only to the nearest
Ah yes, but why a) would you want to only adjust it that way, an b) why not do a fit and figure outexactly what the rate of the clock is and how far out it is, and correct that, rather then simply "shove the rate a bit higher if you see the clock time is behind time now, and a bit slower if you see the clock is ahead." (which is what ntp does). > second by eye. If you want the clock to loose/gain one second per day then > it will take you one day (at best) to adjust the time as it would take that > long to detect an error. It you want to adjust the rate such that it only > gains one second per month it would take a month before you'd know if you > got it right. You have to remember that NTP works be adjusting the rate, > faster or slower and tried hard to never "jump" the time. The only why for > anyone to know if the rate is right is to wait, greater accuracy requires > longer a wait. But ntpd has no compunction about jumping the time if it is out by 125 ms. It does not try very hard not to jump the time at all. > > NTP works kind of like this. Small errors take a long time to detect and > smaller errors take even longer to detect. So up to a point NTP's error no, an error in offset of 1 usec can be detected immediately if you have a good reference (and almost never if you do not) . And an error in rate of 1usec/s can be detected easily within a minute. > gets smaller the longer you wait. The details depend on your Internet > connection and the distance to the server(s). For most people a "few" hours > gets you "close" and you are almost as good as you will be after a half day. > After 24 hours improvement is unlikely. > > So the conservative answer is "24 hours" but for most practical purposes you > are "good enough for file system time stamps and the like" after 1 or 2 > hours. Depends on your accuracy requirements. > > > _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
