Differences between the two Citrix licensing models and a “secret” command to release licenses


BTW (By the way), the “secret” command to release licenses is called: UDADMIN and it is explained further below (it applies for the User Device Licensing model only; you have to run it locally on the license server).

Citrix uses two different licensing models for its products:
User device licensing model and Concurrent Licensing Model

Citrix makes the following comparison statement between the two models:

“Concurrent licensing is based on concurrent device connections. A license is only considered “in use” when a device has established an active connection. This licensing model is best for occasional or anonymous usage. Whereas, under the user or the device model, the licenses remain assigned to the user or the device and are not available for reassignment until 90 days of inactivity have passed” (source: CTX128013)

Concurrent licensing is the traditional model that has been around for many years now. In a nut shell, it is basically this:

A user logs in and launches an application. One license is checked out of the licensing pool. After using the application, the user closes the app and the session ends. The license is checked back in into the licensing pool and can be used by another user who decides to log on after the first user logs off
In very , very simple terms that is a example of concurrent licensing model

A good use simplistic case of the Concurrent model:
Scenario: Your company bought 50 concurrent licenses of XenApp for its 150 employees where each employee has his/her respective workstation, totaling 150 devices.

Let say this company has its 150 employees working 24×7 divided in three 8hr shifts with 50 employees each shift. At any moment you can only have 50 concurrent users accessing the devices and the published apps.

So, you can have 50 licenses to accommodate the 50 users of the first shift concurrently. Once they end their shift and log out of their workstations, all 50 licenses are now available again. The next 50 2nd shift employees start working and log on to their machines. The same 50 licenses available for the 1st shift employees are now available for the 2nd shift employees. They repeat the procedure (check out their licenses when logging on and open their apps and check back in their licenses when they log off and end their shift). The 3rd shift repeats the same procedure all over again. Conclusion: With 50 Citrix licenses, 150 employees were able to access Citrix resources 24 hours day.

For this example, using the Xen Desktop User Device model things change quite a bit. (Let’s make the assumption that each one of the 150 users has a unique workstation (or a “device”))

Once the 50 employees of the 1st shift log on to their workstations and launch their apps, those licenses will be retained for 90 days. So for example, if one user logs only once and gets fired or quits his job at the end of the first day, that user license will be retained for the next 90 days until it is released automatically, (if that user account never logs in again). The 2nd shift employees will also use a different set of 50 licenses and so are the 3rd shift employees. In this example, you really need 150 Xen Desktop User licenses to accommodate the 150 users accessing their 150 devices. So if you don’t want to buy 150 licenses, the alternative here is to delete the 50 licenses at the end of each shift manually, one by one or via a batch file or via some script.
If you are using the User Device model you can access the Licensing Server, open a CLI prompt, navigate to the folder C:\program files (x86)\citrix\Licensing\LS and issue the command “udadmin” to:

1. list the user and devices allocating the licenses (c:\>udadmin -list)
2. Release a device (C:\>udadmin -f XDT_ENT_UD -device [device name] -delete
3. Release an user (c:\>udadmin -f XDT_ENT_UD -user [username] -delete
4. List all features, versions, counts of licenses, and the users and devices (c:\>udadmin -list -a)

Although it appears that the Concurrent model is more beneficial than the User Device Model, based on the example above (note the 50 users can be considered “occasional users” (using the Citrix verbiage), since they logon no more than 8hrs per day) ; there are many use cases where the User Device model fits better the environment. To read more about it, please read this Citrix CTX article that explains in details the differences between the two models:
FAQ XD 5.x Licensing

If you want to know the proper syntax of the UDADMIN command and some examples see this Citrix E-Docs link on UDADMIN

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