SAP HANA license.

Like all SAP products,we need an valid license to run SAP HANA for production systems.
SAP HANA licenses are of following types:
  • Temporary
  • Permanent -  Enforced and Unenforced
Temporary License: A temporary license is installed by default with system install, this license if valid for 90 days and upon expiration the HANA system is locked down.
Permanent: SAP provides this license upon request , this is a permanent license(no expiry date) and can also  be granted till certain duration.  Once this period is over the license will get expired and a temporary license will be installed automatically for 28 grace period.

Permanent license are of two types:
Enforced: HANA license are based on the memory usage, for example you can install a 1 TB memory HANA system but can only license it for 256 GB usage. If the system usage is increased over licensed amount then the system will locked down if the license is "Enforced".
Unenforced: The system will issue a warning upon over usage of SAP HANA licensed memory amount but it will not get locked down.
SAP HANA License Life Cycle

How to check SAP HANA license?
Requirement: You want to check SAP HANA license validity in SAP HANA system.
Prerequisite: We need database user with LICENSE ADMIN system privilege assigned.

Steps:
Connect to the required system via HANA Studio
Open Administration perspectiveYou can open it from Window > Open > Perspective > Administration Console
In Administration perspective ,open the context menu(shown below) and select "Properties".
SAP HANA license Context menu

Now , select "License" in following screen and you will see the license and system information.
SAP HANA license and system information

Above information can also be retrieved by executing following query.
 SELECT * FROM "SYS"."M_LICENSE";
 SAP HANA license check by SQL

How to check if the installed HANA license is enforced or unenforced ?
Execute following query and if the "Enforced" column value is "False" then your license is not enforced.
 SELECT EXPIRATION_DATE,ENFORCED,PERMANENT,LOCKED_DOWN FROM "SYS"."M_LICENSE";
SAP HANA license SQL check
Reference: 
SAP Note# 1644792 - License key/installation of SAP HANA platform edition
https://help.sap.com