[ntp:questions] NTP-PPS standalone operation: How to ignore network interface changes?

Joachim Fabini Joachim.Fabini at tuwien.ac.at
Fri Jun 12 08:07:36 UTC 2015

Does anyone know how to stop ntpd to listen to local network interface
changes? That is, I want ntp to listen exclusively to the local GPS/PPS
signal (server and ignore all other network interfaces,
messages, events, etc.

I'm using ntp on a Linux-based box for accurate time synchronization.
Accuracy requirements are in the order of 10 microseconds to UTC which
works well with my GPS/PPS system. Adding external time servers does not
help. This is why I run ntp in stand-alone mode, only relying on the
GPS/PPS signal.

However, whenever I bring up or tear down an interface on the local
host, ntp starts its internal algorithms and the ntp time offset
increases substantially. It takes tens of minutes (or even hours) until
the offset is again within required limits.

My ntp.conf has no server lines except server and the
corresponding fudge entry. I tried many solutions without any success
like (the ones I expected to work):
interface ignore all
restrict default kod notrap nomodify nopeer noquery

Still, ntp listens on interface changes and starts its offset adaption
on changes. I understand that this is a highly valuable feature in most
ntp configurations (avoids the need that all network interfaces are up
when starting ntp) but in my case it's a real pain.

Any idea how I can get rid of this behavior (without starting to dig
into the ntp sources)?

tia, br Joachim

More information about the questions mailing list