Microsoft Visual Basic 2008 : Using WMI with Services

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We will use WMI to gather information about the local system and then use that information to create an entry in the Application log. Your service can also use the data collected to perform actions, such as terminating processes and rebooting the system, or even on remote systems to start processes or log events.

You can use WMI and Microsoft Visual Basic 2008 to create self-monitoring services that report information to administrators, or log events that are being monitored for by other enterprise applications. You can create these services, or agents, that run on the local computer, perform tasks, report results, and act as a very powerful tool. In some cases you can handle these situations with an out-of-the-box solution. However, sometimes these solutions are costly and require maintenance, licensing, and external training. Self-produced solutions can help you create a rich set of operational tools.

Suppose you want to monitor a system’s available memory and report an error if that memory drops below a certain point. You could easily do this with other existing applications, but the steps taken in reaction by those applications may not fit with your needs. Some solutions have both client and server pieces: You can use the server piece to monitor for SNMP trap messages or NT Events logged by your service and then have it react to those messages. In some of these instances, purchasing client or agent licenses may cost extra. If you could produce this agent yourself, knowing that it is a required component of your monitoring, you could save your company time and money. Because the code is yours, you could more easily distribute it or share and reuse it elsewhere. Documentation and support is also more readily available with internal resource knowledge of the application.

The great thing about WMI is that it comes with Windows XP, the Microsoft Windows 2000 server series, the Microsoft Windows 2003 server series, and other Microsoft operating systems. In some cases, you must install specific service packs to obtain this, but it is a default for Windows XP, Windows 2000, and Windows Server 2003. 

WMI Architecture

The WMI implementation architecture is fairly simple in terms of how it is exposed. WMI creates computer- and application-level classes that provide access to built-in system and application-defined objects.

To access WMI you have to know the fully qualified domain name (FDQN) of the object you are attempting to access in WMI terms. Everything starts at the root node or namespace for a given object. You first connect to that root node and then use that interface to connect, add, retrieve, update, and execute methods and properties that are exposed by classes that exist in the given node or namespace.

Whether you are using the Management namespace from .NET or the COM interfaces exposed by Windows and WMI, the usage and syntax are very similar. The technology used to connect to WMI doesn’t necessarily create any WMI syntax differences, but it does create code-specific differences because the objects you are using to talk to WMI are implemented differently.

Adding the WMI Class Reference

When you use the WMI object model in non-.NET languages, it is used through COM interfaces and classes. When you use WMI with .NET, you can use the System.Management namespace. If the Management namespace is not part of your project you will need to add its reference in your project. Select Project, select Add Reference, and then select the System.Management .NET DLL. Now we can create the WMI class.

Once you have added the System.Management reference to the project you will need to add an Imports System.Management declaration to the top of the Tutorials.vb class.

Creating the Generic WMI Class

We are going to use a generic WMI class to query information about the current processes running on our system and then record that information into the Application log. In later sections we will monitor for certain applications and then take actions based on those applications. Listing 8-1 shows the code required for our WMI generic class.

Listing 1. Generic class with Microsoft WMI support.
Imports System.Management
Imports System.Threading
Public Class WMI
  Private m_Error As String = Nothing
  Private m_Scope As ManagementScope = Nothing
  Private m_Path As ManagementPath = Nothing
  Private m_MOC As ManagementObjectCollection = Nothing

  Public Sub New()
  End Sub

  Private Const Processes As String = "Select * from Win32_Process"
  Private Const BootInfo As String = "select * from Win32_BootConfiguration"
  Private Const LogicalDisk As String = "select * from Win32_LogicalDisk"
  Private Const SystemInfo As String = "select * from Win32_ComputerSystem"

  Public Enum Management_Query_Type
    Processes = 1
    LogicalDisks = 2
    BootInfo = 3
    SystemINfo = 4
  End Enum

  Public Function Connect(ByVal pszServer As String) As Boolean
        If Not m_Path Is Nothing Then
                m_Path = Nothing
            Catch ex As Exception
                m_Error = ex.ToString
            End Try
        End If
        If Not m_Scope Is Nothing Then
                m_Scope = Nothing
            Catch ex As Exception
               m_Error = ex.ToString
            End Try
        End If
        m_Path = New ManagementPath("\\" + pszServer + "\root\cimv2")
        m_Scope = New ManagementScope(m_Path)
        Return True
    Catch ex As Exception
        m_Error = ex.ToString
        Return False
    End Try
End Function

Public Function Query( _
    ByVal pszQuery As String, _
    Optional ByVal iType As Management_Query_Type =
     Management_Query_Type.Processes) _
    As ManagementObjectCollection
      Dim tmpQuery As New ObjectQuery
        If Not pszQuery Is Nothing Then
            tmpQuery.QueryString = pszQuery
            Select Case iType
                Case Management_Query_Type.BootInfo
                    tmpQuery.QueryString = BootINfo
                Case Management_Query_Type.LogicalDisks
                    tmpQuery.QueryString = LogicalDisk
                Case Management_Query_Type.Processes
                    tmpQuery.QueryString = Processes
                Case Management_Query_Type.SystemINfo
                    tmpQuery.QueryString = SystemInfo
                Case Else
                    m_Error = "Invalid Query Type"
                    Return Nothing
            End Select
        End If
        Dim MOS As ManagementObjectSearcher = New
  ManagementObjectSearcher(m_Scope, tmpQuery)
        m_MOC = MOS.Get()
        tmpQuery = Nothing
        Return m_MOC
    Catch ex As Exception
        m_Error = ex.ToString
          Return Nothing
      End Try
  End Function

  Public Function GetError() As String
          Return m_Error
      Catch ex As Exception
          Return ex.ToString
      End Try
  End Function
End Class


The code in Listing 1 will connect to the local or remote server and then run the predefined query of your choice, returning the result set to the caller. The class exposes a simple <Connect> method that will connect to the local or remote WMI RPC services at the root specified and return an error if it fails. Then the class provides a simple method called <Query>, which can retrieve information about a query, either passed into the method or from the predefined WMI queries.

You can use WMI for monitoring and reporting in many ways. We are going to use WMI to look at specific system information. In our WMI class we don’t have specific methods to process the data that we retrieve. This is because although we could create a generic wrapper around all the WMI object and property data collections, we are only focusing on a small subset of specific information. First let’s review how WMI works so that you can better understand what you can do with it.

Understanding WMI Classes and Their Uses

WMI is a set of classes that represent system information in the form of objects, such as a logical disk, a CD-ROM, or even your physical memory. This data that WMI retrieves comes from another interface that WMI inherits from. However, although WMI lists nearly all of the properties of an object from its base or parent class, in some cases the data or property is not supported. This means that you can query for that data, but when you try to access the property data you get what WMI calls a DbNull. This is similar to what you would get in a SQL database query when a field is set to NULL.

Specific WMI and Custom Classes

The WMI classes are not just those that come with the base operating system. Developers can create a WMI interface for an application and expose those methods and properties. This means that our generic WMI class can pull data from any WMI-compatible object. 

Listing 2 shows the Win32_ComputerSystem class definition.

Listing 2. WMI Win32_ComputerSystem root node implementation.
class Win32_ComputerSystem : CIM_UnitaryComputerSystem
  uint16 AdminPasswordStatus;
  boolean AutomaticResetBootOption;
  boolean AutomaticResetCapability;
  uint16 BootOptionOnLimit;
  uint16 BootOptionOnWatchDog;
  boolean BootROMSupported;
  string BootupState;
  string Caption;
  uint16 ChassisBootupState;
  string CreationClassName;
  sint16 CurrentTimeZone;
  boolean DaylightInEffect;
  string Description;
  string DNSHostName;
  string Domain;
  uint16 DomainRole;
  boolean EnableDaylightSavingsTime;
  uint16 FrontPanelResetStatus;
  boolean InfraredSupported;
  string InitialLoadInfo;
  datetime InstallDate;
  uint16 KeyboardPasswordStatus;
  string LastLoadInfo;
  string Manufacturer;
  string Model;
  string Name;
  string NameFormat;
  boolean NetworkServerModeEnabled;
  uint32 NumberOfProcessors;
  uint8 OEMLogoBitmap[];
  string OEMStringArray[];
  boolean PartOfDomain;
  sint64 PauseAfterReset;
  uint16 PowerManagementCapabilities[];
  boolean PowerManagementSupported;
  uint16 PowerOnPasswordStatus;
  uint16 PowerState;
  uint16 PowerSupplyState;
  string PrimaryOwnerContact;
  string PrimaryOwnerName;
  uint16 ResetCapability;
  sint16 ResetCount;
  sint16 ResetLimit;
  string Roles[];
  string Status;
  string SupportContactDescription[];
  uint16 SystemStartupDelay;
  string SystemStartupOptions[];
  uint8 SystemStartupSetting;
  string SystemType;
  uint16 ThermalState;
  uint64 TotalPhysicalMemory;
  string UserName;
  uint16 WakeUpType;
  string Workgroup;


The great thing about this class is that we can use it to query every computer on our network and gather information directly from the system, then use that information to compare it to information that administrators or the purchasing department has compiled. You could use this information, such as TotalPhysicalMemory, to verify that the equipment has what it is supposed to. It will also help to show what memory the operating system sees compared to how much memory is installed in the system


It is possible to modify the boot.ini to tell the Windows operating system to only use a certain amount of the total memory installed on the server motherboard.

We will use WMI to query Name, Domain, Status, NumberOfProcessors, and TotalPhysicalMemory and then report this information to the Application log.

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