[root@rhel8 ~]# subscription-manager register --username=xxx

[root@rhel8 ~]# yum install vim
Updating Subscription Management repositories.
This system is registered to Red Hat Subscription Management, but is not receiving updates. You can use subscription-manager to assign subscriptions.
Error: There are no enabled repositories in "/etc/yum.repos.d", "/etc/yum/repos.d", "/etc/distro.repos.d".

[root@rhel8 ~]# subscription-manager attach --auto
Installed Product Current Status:
Product Name: Red Hat Enterprise Linux for x86_64
Status:       Subscribed