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 virtual void OnStart (
	string[] args
protected void OnStart (
	String[] args
protected function OnStart (
	args : String[]



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 when the computer reboots by setting the StartType on the service's installer. 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.

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 override void OnStart(string[] args)
            IntPtr handle = this.ServiceHandle;
            myServiceStatus.currentState = (int)State.SERVICE_START_PENDING;
            SetServiceStatus(handle, myServiceStatus);

            // Start a separate thread that does the actual work.

            if ((workerThread == null) ||
                ((workerThread.ThreadState &
                 (System.Threading.ThreadState.Unstarted | System.Threading.ThreadState.Stopped)) != 0))
                EventLog.WriteEntry("SimpleService.OnStart", DateTime.Now.ToLongTimeString() +
                    " - Starting the service worker thread.");

                workerThread = new Thread(new ThreadStart(ServiceWorkerMethod));
            if (workerThread != null)
                EventLog.WriteEntry("SimpleService.OnStart", DateTime.Now.ToLongTimeString() +
                    " - Worker thread state = " +
            myServiceStatus.currentState = (int)State.SERVICE_RUNNING;
            SetServiceStatus(handle, myServiceStatus);


  • Full trust for the immediate caller. This member cannot be used by partially trusted code. For more information, see .

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

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0