If you are getting the following response when trying to use the yum or dnf command,
This system is not registered with an entitlement server. You can use subscription-manager to register.
Try editing the subscription-manager.conf file, and disable it by changing enable=1 to enable=0
sudo nano /etc/yum/pluginconf.d/subscription-manager.conf
After you may run
yum clean
That should take care of the problem.