Bug#2982: xntp calls ntpdate at start
xntpd calls ntpdate from /etc/init.d/xntp. This bypasses the
authentication settings in /etc/ntp.conf, and it also defeats the sanity
check in xntpd that refuses to step the clock more than 1024 seconds, and
the cross-checks when multiple servers are configured.
It's not necessary to run ntpdate on every boot, since the time will be set
from the CMOS clock, which will be kept accurate by the kernel while NTP is
running. If Linux is down for long enough for the clock to drift
substantially, xntp will step the clock by itself after determining the
correct time based on *authenticated* chimes from *every* NTP server.
Probably it is a good idea to run ntpdate from postinst when the package is
first installed (not upgraded), but once you have configured an NTP
environment, you should never need to touch it again.