Some of us prefer the yum-cron method of automatic updates. CentOS 6 shipped out with a daemonized updater that may not suit your particular needs. Here is the proper procedure for switching over to yum-cron:
yum install yum-cron chkconfig yum-cron on chkconfig yum-updatesd off service yum-cron start service yum-updatesd stop
You should then run a ‘yum update’ to make sure you’re currently up to date. This will also show you that there are no conflicts. Remember, if there are conflicts yum won’t be able to update. This means that yum-cron won’t be able to auto update you either. Resolve ANY conflicts before assuming your system will be staying up to date.