15.4. Setting Up chrony for Different Environments

15.4.1. Setting Up chrony for a System Which is Infrequently Connected

This example is intended for systems which use dial-on-demand connections. The normal configuration should be sufficient for mobile and virtual devices which connect intermittently. First, review and confirm that the default settings in the /etc/chrony.conf are similar to the following:
driftfile /var/lib/chrony/drift
commandkey 1
keyfile /etc/chrony.keys
The command key ID is generated at install time and should correspond with the commandkey value in the key file, /etc/chrony.keys.
Using your editor running as root, add the addresses of four NTP servers as follows:
server 0.pool.ntp.org offline
server 1.pool.ntp.org offline
server 2.pool.ntp.org offline
server 3.pool.ntp.org offline
The offline option can be useful in preventing systems from trying to activate connections. The chrony daemon will wait for chronyc to inform it that the system is connected to the network or Internet.

15.4.2. Setting Up chrony for a System in an Isolated Network

For a network that is never connected to the Internet, one computer is selected to be the master timeserver. The other computers are either direct clients of the master, or clients of clients. On the master, the drift file must be manually set with the average rate of drift of the system clock. If the master is rebooted it will obtain the time from surrounding systems and take an average to set its system clock. Thereafter it resumes applying adjustments based on the drift file. The drift file will be updated automatically when the settime command is used.
On the system selected to be the master, using a text editor running as root, edit the /etc/chrony.conf as follows:
driftfile /var/lib/chrony/drift
commandkey 1
keyfile /etc/chrony.keys
initstepslew 10 client1 client3 client6
local stratum 8
manual
allow 192.0.2.0
Where 192.0.2.0 is the network or subnet address from which the clients are allowed to connect.
On the systems selected to be direct clients of the master, using a text editor running as root, edit the /etc/chrony.conf as follows:
server master
driftfile /var/lib/chrony/drift
logdir /var/log/chrony
log measurements statistics tracking
keyfile /etc/chrony.keys
commandkey 24
local stratum 10
initstepslew 20 master
allow 192.0.2.123
Where 192.0.2.123 is the address of the master, and master is the host name of the master. Clients with this configuration will resynchronize the master if it restarts.
On the client systems which are not to be direct clients of the master, the /etc/chrony.conf file should be the same except that the local and allow directives should be omitted.