Hi there thun
You would need installation number.
The Red Hat Enterprise Linux 5 Installation Number is a 16-character hexadecimal text string used during the installation process. The installation number enables a user to install the full set of supported packages included with the subscription. For a limited set of Red Hat Enterprise Linux subscribers, the installation number is also used to activate subscriptions for additional Red Hat products and services. It replaces the Subscription Number from earlier versions of Red Hat Enterprise Linux.
The installation number for the Red Enterprise Linux 5 subscription can be found in several places, including:
1. The new subscription activation email, received by your Red Hat Network Organization Administrator (the user who first established the Red Hat account) or your company's purchasing contact named on the order. The subject line for the new subscription activation email is the New Subscription Activation key of the product.
2. Red Hat Subscription Management:
3. Red Hat Customer Service: