[ntp:questions] ntpd -qg VS ntpd in Linux client ?

Steve Kostecke kostecke at ntp.isc.org
Sat Apr 28 20:22:52 UTC 2007


On 2007-04-28, Riccardo Castellani <castellani.riccardo at tiscali.it> wrote:

> I'm interesting to align time in my four DB servers (HP-UX o.s.) of my
> company. But I'm not just sure to use ntpd -qg or ntpd as service.

ntpq -gq only slews/steps the clock once. After that the clock will
drift.

ntpd (as a daemon) continuously disciplines the clock to steer in in to
synchronization with UTC (or some other timebase).

> if I use "ntpd -qg":
>
> 1 - if server time is backward real time, does "ntpd -qg" slew time
> immediately ?
>
> 2 - if server time is forward real time (< 128 ms), does "ntpd -qg"
> slew time immediately ?
>
> 3 - if server time is forward real time (> 128 ms), does "ntpd -qg"
> sleps time ? but Does it complete its job before exit ( also if it
> occurs several days ) For example if offset = 120s, "ntpd -qg" exits
> after local time is ok that is after several days ?

The default behavior of ntpd is to slew the clock if the offset is 128ms
or less and step the clock if the offset is more than 128ms. There is no
difference between single-setting (w/ -gq) and daemon mode.

> 4- If I have offset = 120s what's difference in using "ntpd" and "ntpd -qg".

ntpq -gq only slews/steps the clock once. After that the clock will
drift.

ntpd (as a daemon) continuously disciplines the clock to steer in in to
synchronization with UTC (or some other timebase).

> 5- what traffic bandwith does ntpd use ? 

Minimal.

ntpd uses 2 packets per remote time server at each poll. The poll
interval starts at 64 seconds and usually increases to 1024 seconds (~17
minutes).

> For my opinion "ntpd -qg" is better for client, while ntpd as service
> it should be run in time server machines.

ntpq -gq sets the clock _once_ so you have use a regular cronjob if you
want to keep the clock from drifting. So you might as well just let ntpd
run all of the time.

-- 
Steve Kostecke <kostecke at ntp.isc.org>
NTP Public Services Project - http://ntp.isc.org/




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