On Linux with systemd it is possible to have multi-sessions on one seat, eg. I have reached the graphical target starting my display manager, login, and then my graphical user session is in place. I can additionally login via ssh or similar – as far as I understood, this is another session.
However, I'd like to have another such graphical session (preferredly via another DM instance) "in background" (from a different TTY and I can perhaps vtswitch to it) that also uses a different configuration (specifically, auto-login to another user). So when I start my computer (eg. via WOL), I'm greeted with a DM to login, and another user is automatically logged in in the background spawning X with a preconfigured setup.
Rationale: This other user should also launch Steam to be available for In-Home Streaming in the network. I'd like to even extend this to have more than just one instance of Steam In-Home Streaming hosts running, with different accounts to be available, but AFAIK Steam doesn't support this use-case.
However, after reading up on the systemd terminology of sessions and seats and display managers, I've no idea whether this is even possible. A workaround idea was to use systemd services, possibly lingering, to start X under a different user from in the background but this didn't lead anywhere. I'm not quite sure which approach to follow or whether any of this could work, if someone with a deeper understanding of sessions could chime in and give their advice, that'd be really great!
Another idea I've been playing around with in my head is to only have one graphical session, but use something like cage, a Wayland kiosk, to spawn a hidden "full-screen" Steam instance that's available to stream from.
