[ntp:questions] Clock time synchronization of four computers

Kennedy, Paul P.Kennedy at fugro.com.au
Mon Jul 9 05:06:00 UTC 2012


Nazim,
If all you need is relative timing, pick a computer as master (a modern
one one you rarely reboot is a good choice), edit the ntp.conf file to
use a series (say 3) of external pool servers.  then goto the other 3
machines, edit the ntp.conf file and point them at you master, NOT the
pool servers.

e.g.
lets say you have 4 pc's

PC1 192.168.1.1 (we will call this the master)
PC1 192.168.1.2 
PC1 192.168.1.3 
PC1 192.168.1.4

PC1 (master on say 192.168.1.1) ntp.conf

server 0.pool.ntp.org
server 1.pool.ntp.org
server 2.pool.ntp.org


PC2 (192.168.1.2) ntp.conf

server 192.168.1.1 minpoll 4 maxpoll 5 iburst prefer
server 192.168.1.3 minpoll 4 maxpoll 5 iburst noselect
server 192.168.1.4 minpoll 4 maxpoll 5 iburst noselect

PC2 (192.168.1.3) ntp.conf

server 192.168.1.1 minpoll 4 maxpoll 5 iburst prefer
server 192.168.1.2 minpoll 4 maxpoll 5 iburst noselect
server 192.168.1.4 minpoll 4 maxpoll 5 iburst noselect


PC2 (192.168.1.4) ntp.conf

server 192.168.1.1 minpoll 4 maxpoll 5 iburst prefer
server 192.168.1.2 minpoll 4 maxpoll 5 iburst noselect
server 192.168.1.3 minpoll 4 maxpoll 5 iburst noselect

this will ensure they all synch up.  the noselect will assist you with
ntpq as you will see all the PC's in the same list and easily assess how
well they align.



-----Original Message-----
From: questions-bounces+p.kennedy=fugro.com.au at lists.ntp.org
[mailto:questions-bounces+p.kennedy=fugro.com.au at lists.ntp.org] On
Behalf Of unruh
Sent: Monday, 9 July 2012 12:25 PM
To: questions at lists.ntp.org
Subject: Re: [ntp:questions] Clock time synchronization of four
computers

On 2012-07-08, Nazmul Islam <nazmul.islam at gmail.com> wrote:
>>
>> Hello,
>>
>> I have not used ntp processing before. I apologize in advance if my 
>> questions seem too novice.
>>
>> I am trying to synchronize the clocks of four computers. The timing 
>> does not have to be accurate but they have to be sync'd with each 
>> other.  An error tolerance of 10-20 ms is acceptable. The computers 
>> are connected to the servers.

Well a good way of synchronizing them is to have them all synchronized
to UTC. Another is to synchronize one to UTC and the others to it as the
server.

>>
>> I installed ntp by typing 'sudo apt-get install ntp' in the terminal.

>> When I typed "sudo ntpq -c lpeer", each computer was found to be 
>> connected to different timing websites.

So what?
They are all probably pool servers and synchronized to UTC. But if you
want something else, edit /etc/ntp.conf and put in the same "server"
lines.


>
>    Therefore, I modified the ntp.conf server list and put the 
> following ones for each of them (I am at NJ, USA):
>
> server nist1-ny.ustiming.org
> server nist1-nj.ustiming.org

Why would you overload a level 1 server?

> server ntp.ubuntu.com
>
>
>> However, each computer is still off. It's hard to find the exact time

>> difference from eye-balling but I can see a clock time difference of 
>> roughly 1-2 second.

No idea what that means, but on each of them use ntpq to look at the
time offset from utc.

You do not tell us what operating system you are using. 
ssh other.computer date;date
will tell you if they are off by seconds. 


>>
>> What should I do to synchronize these computers?

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