5 NTP servers in ntp.conf

[MarioT]

Hello,

Does CentOS/RedHat support 5 (or more) ntp servers in npt.conf?
By default there are four of them defined which should be enough
but I have 5 available and customer wants them all.
man ntp.conf does not mention how many we can define.

Thanks
Mario

[avij]

Yes, you can have five upstream NTP servers defined in your ntp.conf, and even more if you want to. It is unlikely you will hit any such limits.

[MarioT]

Thanks a lot.

[CElliott]

FWIW, the optimal number of servers, according to the illuminati, is 9. However, as a practical matter, with a large number of servers you may experience "time islands," where 5 servers will coalesce around one time value and 4 around another, perhaps a millisecond or two different. For the most accurate time with NTPD, choose several servers from the lists at http://www.ntp.org and/or http://tf.nist.gov/tf-cgi/servers.cgi# that are ELECTRCALLY CLOSE to your location. That is, using NTPQ or the Meinberg NTP Monitor, pick several servers that have the lowest delay (and jitter). It can take several days to determine these values, and the only constant is change. NTPD's error tends to be correlated with delay. With a broadband Internet connection, you can expect 10s of microseconds offsets if you choose the servers carefully.