Check the clock synchronization in RAC Environment

You have three options for time synchronization between cluster nodes:

• Windows Time service
• An operating system configured network time protocol (NTP)
• Oracle Cluster Time Synchronization Service

Oracle Cluster Time Synchronization Service is designed for organizations whose cluster servers are unable to access NTP services. If you use NTP, then the Oracle Cluster Time Synchronization daemon (ctssd) starts in observer mode. If neither NTP or the Windows Time service is found, then ctssd starts in active mode and synchronizes time among cluster members without contacting an external time server.

Note: Oracle Clusterware 12c Release 1 (12.1) is automatically configured with Cluster Time Synchronization Service (CTSS). The CTSS service does not have command interface, it starts with Oracle High Availability Services daemon (ohasd)

Check the clock synchronization service working:

crsctl check ctss
CRS-4700: The Cluster Time Synchronization Service is in Observer mode.

Note: Observer means – Time sync between nodes is taken care of by NTP
Active means – Time sync between nodes is taken care of by CTSS

Sync the clock on all nodes:

cd $GRID_HOME/bin>cluvfy comp clocksync -n all

Refer:https://docs.oracle.com/en/database/oracle/oracle-database/12.2/cwlin/setting-network-time-protocol-for-cluster-time-synchronization.html#GUID-D2CDFAC3-4CE2-4E56-B34F-81D0FD20CEFA