[taway098123]

I'm sorry about the throwaway, it's a long story.

You're crossing a security boundary trying to access other users' GUI programs. The session bus is for programs that are private to the user's session. Accessing that is mostly equivalent to logging in as that user, you're not supposed to take control of all their programs as another user.

I don't really understand your solution, the problem doesn't go away when you use a Unix socket. You're still crossing a security boundary and now you have to build in those access controls into your program. If you don't really care about the security aspect it would be just as easy to tell the user to grant you access to the dbus socket for their session bus, or run another dbus instance under a different user and control access to that socket. You can publish the same interface on multiple buses at once, and build in your own access controls too.