ntpd fails on boot

[Mark Andrews]

In message <20101218220244.GA19039 at icarus.home.lan>, Jeremy Chadwick writes:
> On Sat, Dec 18, 2010 at 11:37:21AM -0700, Dan Allen wrote:
> > 
> > On 14 Dec 2010, at 5:47 PM, Jeremy Chadwick wrote:
> > 
> > > Anyway, many people are using the below with success.
> > 
> > Sorry to say that netwait did NOT in the end fix the problem.
> > 
> > I however discovered that if I put
> > 
> >   synchronous_dhclient="YES"
> > 
> > into my /etc/rc.conf file, that over many days & reboots now has
> > been delivering reliable networking such that ntpd always works.
> > 
> > Thanks again to everyone for their help.
> 
> For DHCP-based clients, yeah, netwait itself isn't sufficient; you'd
> need to use synchronous_dhclient as you discovered.
> synchronous_dhclient will accomplish the same thing as netwait for
> DHCP-based clients.
> 
> Explanation: dhclient will sit and wait until DHCP is fully negotiated
> before continuing on with remaining rc scripts.  The negotiation
> involves packets going back/forth between the client and server on UDP
> ports 67 and 68, which obvious acts as a validator that traffic is
> flowing across the interface.
> 
> I'll add a comment to the top of the netwait script noting that it
> should be used for environments where the system is not using DHCP
> (configured static IPs in rc.conf), and mention for DHCP-based clients
> to use synchronous_dhclient instead.

My solution was to start/re-start ntp using /etc/dhclient-exit-hooks
whenever the IP address changed.

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org