You should synchronize your system time between your RAC nodes and even for your primary and standby database server by enabling the NTP daemon. You should enable NTP with the –x option to allow for gradual time changes, also referred to as slewing. This slewonly option is mandatory for Real Application Clusters (RAC), but is also recommended for Data Guard configurations. To setup NTP with the –x option, you need to modify the /etc/sysconfig/ntpd file and add the desired flag to the OPTIONS variable, and restart the service with the “service ntpd restart” command.

# Drop root to id 'ntp:ntp' by default.
#OPTIONS="-u ntp:ntp -p /var/run/ntpd.pid -g"
OPTIONS="-x -u ntp:ntp -p /var/run/ntpd.pid"

You can check your current NTP configuration by checking the process status and filtering on the ntp daemon. In the example below, we will start the ntpd service and check to confirm that the settings are correct with the ps command:

[root@rac1 sysconfig]# service ntpd start
Starting ntpd:                                             [  OK  ]

[root@rac1 sysconfig]# ps -ef |grep -i ntp
ntp       3496     1  0 10:38 ?        00:00:00 ntpd -x -u ntp:ntp -p /var/run/ntpd.pid
root      3500  2420  0 10:39 pts/1    00:00:00 grep -i ntp

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