CentOS auto update configuration

Reference:
Stopping automatic updates
Enabling automatic updates in Centos 6 and Red Hat 6

CentOS 4.x:
chkconfig yum on
service yum start

CentOS 5.x:
chkconfig yum-updatesd on
service yum-updatesd start

CentOS 6.x:
yum -y install yum-cron
/etc/init.d/yum-cron start
chkconfig yum-cron on