在RHEL系统中注册和使用subscription是两个过程：
NOTE: With Red Hat Subscription-Manager, registration and utilization of a subscription is actually a two-part process. First register a system, then apply a subscription.
可以使用下面命令一次完成两个过程：
# subscription-manager register --username <username> --password <password> --auto-attach
在我的RHEL 7.2系统上执行上述命令：
# subscription-manager register --username=xxxx --password=xxxx --auto-attach
Registering to: subscription.rhn.redhat.com:443/subscription
The system has been registered with ID: 333486bb-xxxxxx
Installed Product Current Status:
Product Name: Red Hat Enterprise Linux Server
Status: Subscribed
然后检查状态：
# subscription-manager list
+-------------------------------------------+
Installed Product Status
+-------------------------------------------+
Product Name: Red Hat Enterprise Linux Server
Product ID: 69
Version: 7.2
Arch: x86_64
Status: Subscribed
Status Details:
Starts: 06/29/2015
Ends: 06/28/2016
接下来就可以使用“yum install”，“yum update”等命令安装和更新软件了，非常方便。
参考资料：
How to Register and Enable Red Hat Subscription, Repositories and Updates for RHEL 7.0 Server；
How to register and subscribe a system to the Red Hat Customer Portal using Red Hat Subscription-Manager；
RHEL : Register Subscription。