16.16. Configure ntpdate Servers

The purpose of the ntpdate service is to set the clock during system boot. This was used previously to ensure that the services started after ntpdate would have the correct time and not observe a jump in the clock. The use of ntpdate and the list of step-tickers is considered deprecated and so Red Hat Enterprise Linux 7 uses the -g option to the ntpd command and not ntpdate by default.
The ntpdate service in Red Hat Enterprise Linux 7 is mostly useful only when used alone without ntpd. With systemd, which starts services in parallel, enabling the ntpdate service will not ensure that other services started after it will have correct time unless they specify an ordering dependency on time-sync.target, which is provided by the ntpdate service. In order to ensure a service starts with correct time, add After=time-sync.target to the service and enable one of the services which provide the target (ntpdate or sntp). Some services on Red Hat Enterprise Linux 7 have the dependency included by default ( for example, dhcpd, dhcpd6, and crond).
To check if the ntpdate service is enabled to run at system start, issue the following command:
~]$ systemctl status ntpdate
To enable the service to run at system start, issue the following command as root:
~]# systemctl enable ntpdate
In Red Hat Enterprise Linux 7 the default /etc/ntp/step-tickers file contains 0.rhel.pool.ntp.org. To configure additional ntpdate servers, using a text editor running as root, edit /etc/ntp/step-tickers. The number of servers listed is not very important as ntpdate will only use this to obtain the date information once when the system is starting. If you have an internal time server then use that host name for the first line. An additional host on the second line as a backup is sensible. The selection of backup servers and whether the second host is internal or external depends on your risk assessment. For example, what is the chance of any problem affecting the first server also affecting the second server? Would connectivity to an external server be more likely to be available than connectivity to internal servers in the event of a network failure disrupting access to the first server?