I believe that yum-cron now comes package with, but if it doesn’t this do the trick.
Upgrade yum first
# yum upgrade yum
Reboot
Check to see if you already have yum-cron – the cron job for updating
# rpm -qa|grep yum-cron
yum-cron-0.6-1.el5.centos
If you need to get yum-cron do
# yum install yum-cron.noarch
To configure yum-cron do
# /etc/init.d/yum-cron start
Check it’s running
# /etc/init.d/yum-cron status
Configure it to run at boot
# /sbin/chkconfig yum-cron on
IT Vomit! 