Automatically update CentOS 7 with yum-cron

Install yum-cron:
```
sudo yum -y install yum-cron
```
Open /etc/yum/yum-cron.conf in your favorite editor and make sure each of the following values are set to ‘yes’.
```
update_messages = yes
download_updates = yes
apply_updates = yes
```

Other optional settings in yum-cron.conf

# Change from 'default' to 'security'
# if you only want security fixes.
update_cmd = security
# For email alerts (recommended):
email_to = you@domain.com 
# If you use a different mail host:
email_host = smtp.domain.com

Start the service:
```
sudo systemctl start yum-cron
```
Enable the service (makes sure it will start again after a reboot.)
```
sudo systemctl enable yum-cron
```