Weird. Maybe you should have chrony come up before then, which would block
the port for ntpdate.
I just tested that. Ntpdate works just fine while chrony is running.
There is no "port to block". Ntpdate doesn't listen on any port, it
only establishes an outbound connection to a remote server (on port
123).
Ntpdate manual says that it will exit if ntpd is running. I don't
know how it knows when ntpd is running, but it hardly matters, because
(presuming that ntpd is started up at the same place as chrony is)
when ntpdate starts, ntpd is *not* running. So it would have the same
issue, that ntpdate slips in and updates the time underneath it.
Hmmm, now I'm gonna have to test that.
Whether using ntpdate or rdate, it does what you want --- quickly get
the date/time as soon as possible after startup. Remember, no RTC so
it has no idea of what the time is when it first boots up. The
problem is that chrony chokes.
Actually, the distro's ntpdate control files do just what you'd want
them to do ---- when the network becomes available, go grab the date
from a time server.