The Windows Management Instrumentation (WMI) API was developed by Microsoft in 1998 in response to the ever-growing need for developers and system administrators to have a common, scriptable API to manage the components of the Windows operating systems. Before WMI, if you wanted to manage some component of the operating system, you had to resort to using one of the component specific Win32 API's, such as the Registry API or Event Log API. Each API typically had its own implementation quirks and required way too much work to do simple tasks. The other big problem with the Win32 APIs is that scripting languages such as VBScript could not use them. This really limited how much an inexperienced programmer or system administrator could do to programmatically manage systems. WMI changes all this by providing a single API that can be used to query and manage the Event Log, the Registry, processes, the filesystem, or any other operating system component.
So you may be wondering at this point: this is a book on Active Directory, so why do I need to care about a system management API? Even if your sole job in life is to manage Active Directory, WMI can benefit you in at least two ways. First, Active Directory runs on top of Windows 2000 or Windows Server 2003. These servers need to be managed (i.e., Event Log settings configured, Registry modified, applications installed, etc.) and monitored (i.e., filesystem space, services running, etc.). You can choose to do all of those tasks manually, or you can use WMI to automate them. For each task you automate, the total cost of ownership to support Active Directory is reduced, and you help ensure your servers stay consistent. The other reason why WMI is important to Active Directory is the direction Microsoft is taking WMI with respect to monitoring and managing any system or application under the Microsoft umbrella. That's right, not only does Microsoft want WMI to be the primary interface to manage and monitor Windows systems, but also any Windows application, including Active Directory. Currently, ADSI provides the primary management interface into Active Directory, but in the Windows Server 2003 release, there are several new WMI hooks into Active Directory to monitor things such as trusts and replication.
In this chapter, we will give a brief introduction to the concepts and terminology behind WMI and then delve into several sample scripts showing how to make use of it. We will cover some system-specific tasks, such as managing services, the Event Log, and the Registry, which should give you a good grounding in some of the fundamentals of WMI. In the second half of the chapter, we will review how WMI can be used to access and monitor Active Directory.
In a single chapter we can only go into so much detail about the internals of WMI. We won't be covering some of the more advanced topics. If you are interested in more information than what this chapter provides, we recommend checking out the MSDN Library or one of the WMI books available on the market. At the time this book was published, you could access the WMI SDK documentation by going to the MSDN Library (http://msdn.microsoft.com/library) and visiting Setup and System Administration Windows Management Instrumentation (WMI) SDK Documentation or by going to the following web page: http://msdn.microsoft.com/library/en-us/wmisdk/wmi/wmi_start_page.asp.