[ntp:questions] ntpd on dial up machine: no DNS resolving => giving up on all servers

Harlan Stenn stenn at ntp.org
Sat Jun 6 22:49:31 UTC 2009

>>> In article <h0enbo$cme$1 at newsreader2.netcologne.de>, Arno Wald <arno.wald at netcologne.de> writes:

Arno> ntpd is started at boot time and automatically can handle interfaces
Arno> that are brought up or down while ntpd is running since
Arno> 4.2.4p0+dfsg-1. But the problem is, that ntpd cannot resolve the
Arno> ntp-server names at startup (because the PC is offline) and gives up
Arno> on them. When the ppp interface is brough up, ntpd does recognize
Arno> this, but does not retry to resolve the servers.

There is an option to have ntpd retry failed DNS lookups for "longer".  This
is in ntp-dev however (which is about to become ntp-4.2.6).

Arno> I cannot find a configuration option to change this. Is there
Arno> something I can do to make ntpd look up the servers again when the PC
Arno> is going online?

Use IP numbers instead of names.

Get a reasonably inexpensive GPS device and use that for time (or if
geographically convenient, one of the radio refclocks).

Arno> An alternative was to (re)start ntpd on ip-up instead of starting it
Arno> at boot time. The problem with this is that (if I am not wrong) ntpd
Arno> does a big time step instead of just little time adjustments
Arno> once. This can make the mail server dovecot stop if time is set back
Arno> by too many seconds. So is there an option to forbid ntpd such a big
Arno> time step at startup?

You really only want to prevent ntpd from stepping the time backwards.

This topic is one for wider discussion.  Ideally, we'd get something useful
out of POSIX or some other standard.  Or we could all agree on a useful spec
and motivate OS vendors and Standards groups to implement it.
Harlan Stenn <stenn at ntp.org>
http://ntpforum.isc.org  - be a member!

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