How to automate the CentOS cluster synchronization time

How do I get the CentOS cluster to automatically sync time? First of all, the machine to connect the outside network, so as to synchronize time from the Internet, this is the first to understand. Well, the main method is as follows:

On a machine other than running NTPD, perform the following:

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# chkconfig--list | grep ntpd

See if the NTPD is powered on from boot (if the display is all off, it indicates that it is not booting), and if it is powered on, it needs to be executed:

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# chkconfig NTPD off

Turn off ntpd, if NTPD is on, ntpdate can't sync time from other servers.

Then add a line at the end of the/etc/rc.local (possibly/etc/rc.d/rc.local in the Debian/ubuntu system):

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Ntpdate xxx.xxx.xxx.xxx

XXX indicates the IP address of the server running NTPD

And then restart it.

How to automate the CentOS cluster synchronization time