PRVF-5439: NTP daemon does not have slewing option “-x” set on node

PRVF-5439: NTP daemon does not have slewing option “-x” set on node

When installing Oracle 11gR2 Grid Infrastructure either the cluster verify utility or the prerequisite checks find that the NTP daemon does not have the slewing option set.

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- PRVF-5439 : NTP daemon does not slewing option "-x" set   on node "ordrac1"   - Cause: NTP daemon on the specified node does not have the   slewing option set   - Action: Shutdown and restart the NTP daemon with the   slewing option set. For more information on the NTP daemon   slewing option refer the NTP daemon's man pages.

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 backwards 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 system is incremented slower until the system clock is in sync with the time on the reference system.

How to set up slewing

Stop the NTP service on the node.

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[root@odrac1 ~]# service ntpd stop Shutting down ntpd:                                        [  OK  ] [root@odrac1 ~]# [/text/] Edit the file /etc/sysconfig/ntpd 1 # 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   # Additional options for ntpdate NTPDATE_OPTIONS=""

Change the line

1	OPTIONS="-u ntp:ntp -p /var/run/ntpd.pid"

to

1	OPTIONS="-x -u ntp:ntp -p /var/run/ntpd.pid"

After saving the file restart the NTP service. Re-execute the cluster verify utility or the prerequisite checks.

slewing in clusters Linux:

In order to keep the system time synchronized with other nodes in an HACMP cluster or across the enterprise, Network Time Protocol (NTP) should be implemented. In its default configuration, NTP will periodically update the system time to match a reference clock by resetting the system time on the node. If the time on the reference clock is behind the time of the system clock, the system clock will be set backwards causing the same time period to be passed twice. This can cause internal timers in HACMP and Oracle databases to wait longer periods of time under some circumstances. When these circumstances arise, HACMP may stop the node or the Oracle instance may shut itself down. 

Oracle will log an ORA-29740 error when it shuts down the instance due to inconsistent timers. The hatsd daemon utilized by HACMP will log a TS_THREAD_STUCK_ER error in the system error log just before HACMP stops a node due to an expired timer. 

To avoid this issue, system managers should configure the NTP daemon to increment time on the node slower until the system clock and the reference clock are in sync (this is called "slewing" the clock) instead of resetting the time in one large increment. The behavior is configured with the -x flag for the xntpd daemon. 

To check the current running configuration of xntpd for the -x flag:

#ps -aef | grep xntpd | grep -v grep

    root  9306258  3866670   0   Nov 12      -  0:17 /usr/sbin/xntpd 

To change with slewing options

[:root:/home/root:] chssys -s xntpd -a "-x"
0513-077 Subsystem has been changed.

To stop ntpd service/deamon:

[:root:/home/root:] stopsrc -s xntpd
0513-044 The /usr/sbin/xntpd Subsystem was requested to stop.

To start ntpd service/deamon:

[:root:/home/root:] startsrc -s xntpd
0513-059 The xntpd Subsystem has been started. Subsystem PID is 13041866.

[:root:/home/root:] ps -ef|grep ntpd
root 13041866  3801266   0 09:36:05      -  0:00 /usr/sbin/xntpd -x