[ntp:questions] ntpdate works, but ntpd doesn't (reach = 0)

Martin Burnicki martin.burnicki at meinberg.de
Thu Feb 12 09:26:09 UTC 2009


David J Taylor wrote:
> Nero Imhard wrote:
>> Martin Burnicki wrote:
>>
>>> Why shouldn't ntpd be run e.g. on a laptop?
>> [...]
>>> And surely this results in the question which has been discussed here
>>>  several times: why does it takes so long for ntpd to adjust an
>>> initial tiny offset of a few milliseconds?
>>
>> In my understanding, ntpd was designed as a tool to discipline clocks
>> of systems that need (or need to provide) very accurate time, and not
>> as a general-purpose clock-setting tool.

The original (x)ntpd has been designed long time ago, when there was much
less computing power than today. Under those circumstances it may make
sense to think about running ntpd on a system, or not.

Today's standard machines are so powerful that ntpd is a tiny application
(in the sense of resource usage, of course not in the sense of the work it
does). It comes by default with many Unix-like distributions which are not
only installed on servers, or if required for academic studies. 

The number of downloads of the Windows installer clearly shows that ntpd
also becomes more and more widespread even in the Windows world, and
presumably not only on servers.

>> The requirements that would mandate the use of full-blown ntpd are
>> mainly found on systems that stay up and connected for long stretches
>> of time (time servers, measurement and monitoring systems, loghosts,
>> file servers, etc.).

Even systems which are running continuously for a long time may need to be
rebooted sometimes, or ntpd restarted, and I'm sure the operators would
appreciate if the time offset will decrease quicklier than it currently
does, which is clearly possible. 

>> There may well be examples of laptop use cases that require full-blown
>> ntpd and where periodic setting using sntp is unacceptable, but I
>> think they are rare.
>>
>> For this reason, I also think that shortening the time it takes ntpd
>> to do its initial adjustment is not very relevant to its (presumed)
>> design goals.
>>
>> N
> 
> Nero,
> 
> I certainly expect to run NTP on my laptops.  Why should I put up with an
> inferior SNTP, loose the ability to retain the drift value between boots,
> or have to learn how to configure two different pieces of software?  On
> the other hand, providing that the time on the laptops is correct to
> within a second, I'm happy.  I'm not looking for much better than 100ms
> accuracy.
> 
> I view NTP as a general purpose tool which should be automatically fitted
> to /all/ systems, but I am willing to accept that it doesn't work as well
> if the system is not permanently switched on.

I absolutely agree. However, this could be enhanced if the initial
synchronization would be done faster, and if that was the case I don't
think this would result in a limitation for those "big" appliances
mentioned by Nero.

Martin
-- 
Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont
Germany




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