[ntp:questions] stepping and slewing

Kevin Oberman oberman at es.net
Thu May 3 15:23:34 UTC 2007


> Date: Thu, 3 May 2007 09:28:57 +0200 (CEST)
> From: "castellani.riccardo at tiscali.it" <castellani.riccardo at tiscali.it>
> Sender: questions-bounces+oberman=es.net at lists.ntp.isc.org
> 
> I hadn't understood what means "stepping" ( applied when offset is 
> greater than 128 ms ), infact I believed clock converged gradually to 
> real time with for example (3 sec for minute) in like manner to slewing 
> method.
> Now I understand that stepping set clock immediately to correct time 
> (both forward and backward) while slewing permit to adjust gradually 
> time at max 0.5 ms /sec rate (ONLY forward). is'tt OK ?
> I'm going to use ntpd -qg to synchronize my Linux DB "clients" because 
> I think today machine clocks are enough accurate and I don't await 
> significant offsets (between real time and local time) from first 
> synchronization, my opinion is to not use service but a program which 
> starts at specific intervals.

This may already have been covered in this thread and, if not, it has
been on this list several times, but, if you want to get the clock
corrected quickly at boot, be sure to add "iburst" to each peer in
ntp.conf. This will greatly speed up the initial setting of the clock as
it will send several ntp polls to the server quickly to get an initial
sync rather than one every 64 seconds.

It usually takes 4 successful polls to sync, so this saves about 4
and a quarter minutes. After the initial burst (iburst), it starts
polling normally.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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