Tableau offers two licensing models: user based and core based. User based licensing requires each active user account to be covered by a license. User-based licenses have a defined capacity, or number of users that it allows. Each user has a unique username assigned to them on the server and is required to identify themselves when connecting to the server. The software may be installed on a single machine or distributed across any number of machines in a distributed environment.
Core based licensing has no constraints on the number of user accounts in the system, but does restrict the maximum number of processor cores that Tableau Server can use. You may install the server on one or more machines to create a cluster, with the restrictions that the total number of cores in all the machines do not exceed the number of cores you have licensed and that all of the cores on a particular machine are covered by the license.
The most common reason for a server that has user based licensing can be unlicensed is an expired product key or an expired maintenance contract. You can see your products keys and add new ones by selecting Start > Tableau Server > Manage Product Keys.
A core based server can become under licensed for a variety of reasons. A common problem is that the primary or a worker machine has more cores than your license allows. When the server is unlicensed you may not be able to continue starting up or administer the server. You can manage your licenses using the Tabadmin command line tool. Follow the steps below to see a list of your licenses and number of cores by machine.
Open a command prompt and type the following: cd C:\Program Files\Tableau\Tableau Server\6.0.6\bin
Then type the following: tabadmin licenses