How to change the NTP Polling interval of NTP server or NTP client ?

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 4
  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6
  • ntp

Issue

  • How to configure minpoll and maxpoll values in /etc/ntp.conf ?

  • How often a RHEL NTP client will poll out to a NTP server?

  • How often does a ntp client synchronize to ntp servers?

  • Is changing the ntp polling interval recommended?

  • What is the default poll interval for NTP?

Resolution

  • Tweaks to the polling interval is not recommended and is discouraged.

  • NTP dynamically selects the optimal poll interval between the values of minpoll and maxpoll, which default to 64 and 1024 seconds respectively and are correct for most environments. This values can be set in /etc/ntp.conf

  • Shorter values are used to correct large errors while longer values are used to refine accuracy.

  • NTP dynamically varies this value as conditions change and requires several days of continuous operation to converge on an optimal adjustment value.

  • From man ntp.conf we have below definition

minpoll <value>
maxpoll <value>
  • These options specify the minimum and maximum poll intervals for NTP messages, in seconds as a power of two.

  • The maximum poll interval defaults to 10 (1,024 s), but can be increased by the maxpoll option to an upper limit of 17 (36.4 h).

  • The minimum poll interval defaults to 6 (64 s), but can be decreased by the minpoll option to a lower limit of 3 (8 s).

  • These option are valid only with the server and peer commands.

Note : Finally, please make sure to restart the ntp service after any change in /etc/ntp.conf as below:

[root@localhost] # service ntpd restart

Root Cause

  • Forcing a poll interval that is more frequent than what NTP would  normally select on its own, hurts accuracy and stability of time on the local system.

  • NTP polling does not directly synchronize the local system  clock to the server clock; rather, a complex algorithm calculates an  adjustment value for each tick of the local system clock

  • Shorter  polling intervals cause NTP to make large but less accurate calculations that never stabilize, causing the local system clock to wander. They are also useful if you want to make sure that your NTP daemon will detect an outage of the NTP peers in less time.

  • Longer  polling intervals allow NTP to calculate smaller tick adjustments that  stabilizes to a more accurate value, reducing wander in the local system  clock.

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