ServiceBase.OnStart Method

When implemented in a derived class, executes when a Start command is sent to the service by the Service Control Manager (SCM) or when the operating system starts (for a service that starts automatically). Specifies actions to take when the service starts.

Namespace: System.ServiceProcess
Assembly: System.ServiceProcess (in system.serviceprocess.dll)

Protected Overridable Sub OnStart ( _
	args As String() _
Dim args As String()

protected void OnStart (
	String[] args
protected function OnStart (
	args : String[]
Not applicable.



Data passed by the start command.

Use OnStart to specify the processing that occurs when the service receives a Start command. OnStart is the method in which you specify the behavior of the service. OnStart can take arguments as a way to pass data, but this usage is rare.

Caution noteCaution:

Do not use the constructor to perform processing that should be in OnStart. Use OnStart to handle all initialization of your service. The constructor is called when the application's executable runs, not when the service runs. The executable runs before OnStart. When you continue, for example, the constructor is not called again because the SCM already holds the object in memory. If OnStop releases resources allocated in the constructor rather than in OnStart, the needed resources would not be created again the second time the service is called.

Services can be set to start automatically when the computer reboots by setting the StartType on the service's installer to Automatic. In such a situation, OnStart would be called at system startup.

OnStart is expected to be overridden in the derived class. For the service to be useful, OnStart and OnStop should both be implemented in your service class.

Process initialization arguments for the service in the OnStart method, not in the Main method. The arguments in the args parameter array can be set manually in the properties window for the service in the Services console. The arguments entered in the console are not saved; they are passed to the service on a one-time basis when the service is started from the control panel. Arguments that must be present when the service is automatically started can be placed in the ImagePath string value for the service's registry key (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\<service name>). You can obtain the arguments from the registry using the GetCommandLineArgs method, for example: string[] imagePathArgs = Environment.GetCommandLineArgs();.

The following example shows an implementation of the OnStart method for a service class derived from ServiceBase. This code example is part of a larger example provided for the ServiceBase class.

    ' Start the service.
    Protected Overrides Sub OnStart(ByVal args() As String)
        Dim handle As IntPtr = Me.ServiceHandle
        myServiceStatus.currentState = Fix(State.SERVICE_START_PENDING)
        SetServiceStatus(handle, myServiceStatus)

        ' Start a separate thread that does the actual work.
        If workerThread Is Nothing OrElse (workerThread.ThreadState And System.Threading.ThreadState.Unstarted Or System.Threading.ThreadState.Stopped) <> 0 Then
            System.Diagnostics.EventLog.WriteEntry("SimpleService.OnStart", DateTime.Now.ToLongTimeString() + _
                " - Starting the service worker thread.")
#End If

            workerThread = New Thread(New ThreadStart(AddressOf ServiceWorkerMethod))
        End If
        If Not (workerThread Is Nothing) Then
            System.Diagnostics.EventLog.WriteEntry("SimpleService.OnStart", DateTime.Now.ToLongTimeString() + _
                " - Worker thread state = " + workerThread.ThreadState.ToString())
#End If
        End If
        myServiceStatus.currentState = Fix(State.SERVICE_RUNNING)
        SetServiceStatus(handle, myServiceStatus)

    End Sub 'OnStart

Windows 98, Windows Server 2000 SP4, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0