Back To Basics 5: Restricting Task Sequence Usage

Often the simplest tips are the best ones, so here is one I have been using pretty much ever since I started working with MDT.

When working as part of a team in the same MDT environment, you can often run into issues when various people are modifying the task sequence, or debugging a process that is part of it. My own method to mitigate this issue is to fork the "official" task sequence, creating my own one, in order to separately realise testing or to simply try something out, before feeding changes back into the main task sequence.

The downside to this method is that, by forking the task sequence, the new forked one also appears in the list of task sequences and thus allows somebody to accidentally run it, possibly causing undesired results to their computer (such as formatting it!). Therefore, in order to prevent this situation, I always introduce some simple validation tasks into the task sequence, typically right at the start. These validation steps perform a simple query to check if a computer is "authorised" to run the task sequence or not. My authorisation method is usually based on the MAC address of the computer, but it really can be any value that you like.

The best thing about this tip is it's simplicity. As you can see in the screenshot below, it only consists of two tasks (the Gather task is actually only required if you have not already run a previous Gather task), and a Run Command Line task. You'll notice that the command line is incorrect. This is intentional and not an error, and if MDT attempts to run this command line it will fail the task sequence execution.


Here are the steps I use to implement this:

  1. Create a new Task Sequence Group called "Authorised Computer Verification".
  2. Add a Gather task (if necessary).
  3. Add a Run Command Line task, with a command line like the one shown above.
  4. On this same task, switch to the "Options" Tab. On this screen you can add your own personalised conditions, or use the same MAC address conditions that I have used, as shown below.

Notice that the condition is actually a negative. Consequently, when a computer runs the task sequence, this task will only execute if the MAC address of the computer does not match one that is in the list. And because the command line of the task is erroneous, MDT will fail at this point, thus preventing the unknown, or unauthorised, computer from continuing.

When working with MDT and Configuration Manager, you could restrict use of a task sequence by only advertising it to a collection built using direct membership. However, there might be situations where you can't or don't want to use this collection method. This tip works equally well in a ZTI environment if you wish to use it that way, however you might need to add an additional "Use Toolkit Package" task before the Gather step.

Finally, there are other methods to achieve the same result, such as using the CustomSettings.ini file; the reason I do it this way is because its implementation is so quick and simple.

This post was contributed by Daniel Oxley, a Senior Consultant with Microsoft Services UK

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