System Center Configuration Manager 2007 : Operating System Deployment - Task Sequences (part 1) - Variables

The New Task Sequence Wizard, available from the context menu of the Task Sequences node, quickly builds one of two default task sequence types or a custom task sequence:

• Build and Capture

• Deploy an Image

These two task sequence types take care of a majority of the scenarios in OSD; however, task sequences are flexible and not limited to what is produced by default. The task sequence editor allows easy customization of the task sequences; you can tailor sequences to the specific OSD needs of an organization—and with a little imagination, software deployment.

The wizard also presents the option to build a custom task sequence; task sequences built using the custom option are initially blank. Figure 1 shows the first screen of the New Task Sequence Wizard.

Figure 1. The New Task Sequence Wizard

To edit a task sequence, right-click it and choose Edit; choosing Properties from the context-menu results in the Properties dialog box of the task sequence and not the task sequence editor. Adding a task is simply a matter of choosing the Add drop-down menu, choosing a task category, and then selecting the task. Each task is customizable and has its own configurable parameters.

1. Variables

Tasks and task sequences are similar to a macro-based programming language or a storyboard where you put together high-level steps and instructions using a graphical tool, without having to know or learn the syntax of the underlying language to take advantage of it fully. Additionally, third parties can add, and have added, tasks extending this pseudo-macro language enhancing what you can do with task sequences.

A major advantage that task sequences have over the traditional software delivery mechanism used in Systems Management Server and now ConfigMgr is that they maintain a state between steps. This state is embodied in a series of built-in variables and custom variables that survive reboots, allowing you to pass data or configuration items from one step to the next. In fact, the task that the task sequence is currently executing is also part of the task sequence’s state. Variables are encrypted for security when transmitted between ConfigMgr and the target system.

Here are the three types of variables available:

• Action— Specify parameters for specific tasks. Nearly all are directly editable using the task sequence editor.

• Custom— Simple name and value pairs that you can define as you see fit.

• Built-in— Mostly read-only, start with an underscore, are generated automatically by the task sequence, and generally describe the environment where the task sequence executes.

The full list of task sequence action and built-in variables is available at http://technet.microsoft.com/en-us/library/bb632442.aspx. Action variables and custom variables can be set in a number of ways:

• Using a Set Task Sequence Variable task.

• Statically assigning them to a specific computer resource.

• Statically assigning them to a collection.

• Using the Microsoft.SMS.TSEnvironment COM object in a script or other COM compliant language. 

• Leaving the value of a collection or computer variable blank (new with ConfigMgr 2007 R2). The built-in task sequence UI prompts the user for values for these empty variables. 

Task sequence variables set by a Set Task Variable task take precedence over computer-specific variables, which in turn take precedence over collection variables. Collection variables propagate down the site hierarchy with other collection settings. You can assign computer variables only at the site the computer is a member of, and they do not propagate up or down a site hierarchy.

You can use variables for the following tasks:

• Conditionally execute tasks.

• Perform string replacement in command lines. (See the example later in this section and Figure 2.)

  Figure 2. Using String replacement in a Run Command Line task

  

• Provide task-specific parameter values. (See the example in this section and Figure 3.)

  Figure 3. String replacement in a task parameter

  

• Perform string replacement in unattended files. 

For string replacement and parameter values, surround the name of the variable with % symbols; for example for a variable named MyCustomVar, use %MyCustomVar%. The task sequence engine replaces this with the value of the variable. As an example, Figure 19.15 shows the Run Command Line task. This figure demonstrates adding an entry to the Registry that you can later utilize to track the deployment version used when creating the system. You can supply the actual version by a collection variable or a preceding Set Task Sequence Variable task.

Figure 3 shows an example of replacing a parameter in a task. This example shows how you can use multiple product keys in a deployment. You can supply the actual product key in a collection variable or a preceding Set Task Sequence Variable task.