[ntp:questions] Why does ntp keep changing my conf file?

David J Taylor david-taylor at blueyonder.co.uk.invalid
Sat Sep 18 05:54:51 UTC 2010

"Daniel Havey" <dhavey at yahoo.com> wrote in message
> So, you think that a PC clock will drift 20-50ms in 5 seconds?  Seems 
> like a lot, but whatever.  Let me see if I've got this right, you tell 
> me I might get say synchronization of ~10ms with ntpd running on a lan 
> with everybody on the same switch or perhaps one switch away?

You can see some PC performance plots running NTP here:


The top three PCs all have a GPS pulse-per-second reference.  PC Pixie 
runs FreeBSD and is within 10 microseconds.  PCs Feenix runs Windows XP, 
and PC Stamsund Windows-7.  Note the jumps exceeding 250 microseconds on 
Stamsund, and the mainly temperature induced drift of the same order (250 
microseconds) on Feenix.

The other PCs are all synched over the LAN, and get synched within about a 
millisecond, with the exception of Gemini which runs a DVB/USB-box 
satellite data receiver getting about 30GB a day.  It runs Windows Vista.

There are also some plots for WiFi-connected PCs, but they some and go and 
are not 24-hour operational:


The NTP settings on all these PCs have been tuned for best performance on 
a LAN using private servers (and hitting those servers rather more 
frequently than one would with public servers).

Perhaps that helps?


More information about the questions mailing list