In Oracle 11gR2 and later version, while installing Oracle clusterware it is required time synchronization across all nodes within a cluster. We can use two different options to setup time synchronization.
1)Operating system configured Network Time Protocol (NTP).
2)Oracle Cluster Time Synchronization Service (ctssd).
If you don't have NTP services started then Oracle Cluster Time Synchronization Service is used. However if you want to use ctssd (Cluster Time Synchronization Service Daemon) service in the cluster, then deconfigure and deinstall the Network Time Protocol (NTP).
In order to deactivate NTP service, you need to follow the following procedures.
i)Stop the existing ntpd service.
# /sbin/service ntpd stop
ii)Disable the service from the initialization sequences so that it does not start during startup.
# chkconfig ntpd off
iii)Remove the ntp.conf file.
# rm /etc/ntp.conf
or,
# mv /etc/ntp.conf to /etc/ntp.conf.bak
Also remove the file /var/run/ntpd.pid which maintains the pid for the NTP daemon.
# rm /var/run/ntpd.pid
When the installer finds that the NTP protocol service is inactive, the Cluster Time Synchronization Service is installed in active mode and synchronizes the time across the nodes.
IF NTP is active on the server, then the Cluster Time Synchronization Service is started in observer mode, and no active time synchronization is performed by Oracle Clusterware within the cluster.
To check whether ctssd is active or not as grid installation owner just issue,
$ crsctl check ctss
If you want to continue using NTP time synchronization service, then you need to modify the NTP initialization file to set the -x flag, which prevents time from being adjusted backward. After you modify it restart ntpd. Following steps demonstrate the procedure on Oracle Enterprise Linux, Red Hat Linux.
i)Edit /etc/sysconfig/ntpd file and add -x flag.
# vi /etc/sysconfig/ntpd
OPTIONS="-x -u ntp:ntp -p /var/run/ntpd.pid"
SYNC_HWCLOCK=no
ii)Restart NTP service.
# /sbin/service ntp restart
On SUSE systems, modify the configuration file /etc/sysconfig/ntp with the following settings.
NTPD_OPTIONS="-x -u ntp"
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