What is slewing?
The NTP daemon will periodically update the system clock with the time from a reference clock. If the time on the reference clock is behind the time on the system clock, the system clock will be set backward in one large decrement. Such swift changes in time can lead to Oracle shutting down the node due to inconsistent timers. To avoid this problem, NTP can be configured to slew the clock. When slewing the clock the time on the system is incremented slower until the system clock is in sync with the time on the reference system.
This post discusses steps to set NTP slewing option on NTP clients so that the service starts with slewing enabled.
1. Stop ntp service:
# service ntpd stop
2. Edit /etc/sysconfig/ntpd file:
# vi /etc/sysconfig/ntpd
The file looks like in the example below:
# Drop root to id 'ntp:ntp' by default. OPTIONS="-u ntp:ntp -p /var/run/ntpd.pid" # Set to 'yes' to sync hw clock after successful ntpdate SYNC_HWCLOCK=no
Change the line “OPTIONS” line from:
OPTIONS="-u ntp:ntp -p /var/run/ntpd.pid"
OPTIONS="-x -u ntp:ntp -p /var/run/ntpd.pid"
4. Start ntp service for the changes to take effect:
# service ntpd start