Red Hat 7 registration

Register and automatically subscribe in one step
Use the following command to register the system, then automatically associate any available subscription matching that system:

$ subscription-manager register --username <username> --password <password> --auto-attach

Attach a specific subscription through the Customer Portal
After registration, you can to assign a subscription to the registered system from the Customer Portal by referring this article.
After this, refresh the information on your machine using the following command. Be sure to run this any time you add or change the attached subscription from the Customer Portal:

$ subscription-manager refresh

System Administration guide:
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/chap-Subscription_and_Support-Registering_a_System_and_Managing_Subscriptions.html

Get information
$ subscription-manager identity

Removing subscription
$ subscription-manager remove --all ?????????