[BUGS] ntpdate/ntpd at startup (was: Dovecot not starting onstartup)

[John Marshall]

On Wed, 23 Apr 2008, 12:31 +1000, John Marshall wrote:
> I've just conducted some experiments...
> 
> With a default server settings in /etc/ntp.conf (i.e. no minpoll, maxpoll or
> other qualifications to the server command), the time from starting ntpd -g
> until the system is stepped to the correct time is 5.5 minutes. This time
> can be reduced by specifying a lower-than-default minpoll. With minpoll 4
> (16s), the time to step reduces to about 1.5 minutes - which is still
> undesirably long.

I meant to include my observation of time-to-synch for ntpd -g. This
explains the times recorded above.

START
 Poll
  Wait minpoll
 Poll
  Wait minpoll
 Poll
  Wait 2 x minpoll
 Poll
SYNCH (.STEP.)
  Wait minpoll
 Poll

> I remembered reading something about burst-mode polling for dialup
> connections and went back to the ntp documentation. I found the iburst
> option for the server configuration command and note that the documentation
> now says that, "It is a recommended option with this command."
> 
>     server ntp.example.com iburst
> 
> If I add iburst to an otherwise default server configuration line, time from
> ntpd -g to synch is only 10s! The iburst sends an initial burst of
> (according to my measurement) 4 polls at 2s intervals. That seems to give
> ntpd enough confidence to take the .STEP. and then we settle down
> immediately to polling at minpoll and gradually increasing intervals as
> normal.
> 
> Wouldn't it be good if iburst was a command-line switch - or, better still,
> if this "recommended option" became a default option? I think I might do
> some poking around on the ntp lists and see what I can find...
> 

-- 
John Marshall