Configuring chrony

Environment

• Red Hat Enterprise Linux 9
• Red Hat Enterprise Linux 8
• Red Hat Enterprise Linux 7

Issue

• Sample configuration for chronyd.
• What are important configuration parameters required to make chronyd work ?

Resolution

Here are few possible configurations for the chronyd service.

1. If you have 4 NTP servers foo.example.net, bar.example.net, baz.example.net, and bat.example.net, your /etc/chrony.conf file could contain the following time sources directives:

               server foo.example.net
               server bar.example.net
               server baz.example.net
               server bat.example.net
   

2. Some other useful directives : driftfile, makestep, rtcsync, and iburst. The smallest useful configuration file would look something like:

               server foo.example.net iburst
               server bar.example.net iburst
               server baz.example.net iburst
               server bat.example.net iburst
               driftfile /var/lib/chrony/drift
               makestep 10 3
               rtcsync
   

3. If using a pool of NTP servers (one name is used for multiple servers which may change over time), it's better to specify them with the pool directive instead of multiple server directives. The configuration file could in this case look like:

               pool pool.ntp.org iburst
               driftfile /var/lib/chrony/drift
               makestep 10 3
               rtcsync
   

To learn more about each of these parameters please refer to the documentation:

• RHEL7: Configuring NTP Using the chrony Suite
• RHEL8: Using the Chrony suite to configure NTP
• RHEL9: Using Chrony

Note : Ensure 123/UDP port is enabled bi-directionally in the firewall.

Root Cause

The default /etc/chrony.conf file can not be used as it is. It must be altered accordingly to include new NTP servers and other directives as needed.

Diagnostic Steps

• Test configuration:

  # timedatectl
  

• Display system time information

  # chronyc tracking
  

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