Yum automatic update
The recipe to update automatically the rpms on the server is the following (Centos 7):
yum install yum-cron
systemctl enable yum-cron.service
systemctl start yum-cron.service
The update is now apply automatically by the cron job.
Change to apply_updates = yes
in /etc/yum/yum-cron.conf
reference: http://itekblog.com/centos-automatic-updates/#CentOS_7x