[ntp:questions] "ntpd -q" is slow compared to ntpdate

Unruh unruh-spam at physics.ubc.ca
Sun Oct 19 18:53:26 UTC 2008

David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:

>Unruh wrote:
>> David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:

>>> The argument there seems to be not that ntpdate is worse than SNTP, but 
>>> that there is an implied promise that it is almost as good as ntpd.  The 
>>> reason for having SNTP is to have something which has no pretensions of 
>>> being anything other than crude.
>> ??? The rfc on sntp seems to say that sntp should be just as good as ntp in
>> disciplining a local clock, it just should not be used as a server (

>The article wasn't talking about SNTP in general (which basically covers 
>anything, other than NTP, using the NTP wire formats), but rather about 
>the minimal SNTP implementation that should be included in the reference 
>implementation package.

I would think that something called sntp, which as you say "which basically
covers anything, other than NTP, using the NTP wire formats" would hold out
far more promise of being "almost as good as ntpd" than does a program called ntpdate 
(based on rdate) whose only purpose is to use the ntp wire protocol to set the time. 

Ie, I do not believe that anyone thinks that ntpdate is as good as ntp (
although claims that you could run ntpdate every hour from a cron job as an
alternative to ntpd may convey that impression-- but that would also be
true of sntp).

ntpdate serves a useful purpose, something which ntpd -g -q does not do
(because for the purpose of setting the clock in a one-shot manner, ntpd is
seriously flawed, especially if the clock is already within 128ms of the
correct time). Now, sntp should be equally seriously flawed, since the
suggestion in the rfc is that it use the same algorithm for clock setting as ntp uses 
I certainly would not overload the name sntp with yet another operating
mode. (sntp should not be used as a server, unless sntp is fed by a
hardware clock, in which case it can be. Now in addition-- sntp should
discipline the phase and frequency of the clock, unless it is used in a
oneshot manner when it should discipline only the phase.) I think it is far
better to have something called ntpdate to act in a oneshot manner, and be
clear that that is all that it is for, than to overload a name  like sntp
with all kinds of incompatible operating modes. 

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