Starting an Application from Windows Service

Question

I am building a Windows service that will watch for specific occurrences of events and disk activity. When such an event occurs my plan is to alert the user to the event via a client app, and provide remediation if necessary. I have (mostly) completed both the client and service components, which work great... unless the client app isn't running.

In short, I am looking for a way to start up the client app from the Windows service via CreateProcess to provide information to the user. However, it appears the service can't even see the file/folder of the client app to execute it. I suspect this is due to the credentials under which the service is running, or maybe due to service level restrictions, but wanted to reach out for some advise before I get into this any deeper.

So, the obvious question first... am I thinking about this clearly? Is the architecture plan sound, or should I look at another method? I would prefer not to re-do any of the work I have already completed, but obviously want to make sure the plan and process is solid.

Question #2, what are the limitations I face with this model? Is there a service account that will allow this level of access?

I am obviously struggling with this right now, so any thoughts or assistance will be greatly appreciated!

Thanks, Kris

Answer 1

As others have mentioned already, you can't (easily) launch an application directly from the service, so I think the easiest way around the problem is to create a process that starts on login and runs with the credentials of the logged in user, eg an app that sits in the system tray, and it opens up a named pipe or a network port to the service. If the service needs to alert the user, it sends a message down that channel and then the client process can either show its own UI or launch an application. Interprocess communication using pipes or ports are the simplest way to deal with the restrictions on session 0 processes.

Answer 2

A Windows service does not have access to the user session in Vista and above, so it is blocked from starting an executable on that session. You can download a white paper from Microsoft that goes into detail: Impact of Session 0 Isolation on Services and Drivers in Windows.

Answer 3

Since Vista, services run in session 0 and the user's desktop is always in a different session. Thus you need to work hard to start a service on the user's desktop.

It can be done but it is pretty tricky. Details can be found here: http://blogs.msdn.com/b/winsdk/archive/2009/07/14/launching-an-interactive-process-from-windows-service-in-windows-vista-and-later.aspx?wa=wsignin1.0