Comment 2 for bug 1350357

The code in seat-unity.c is actually saying "this seat type is capable of user switching" (the name is very misleading). Also note that the normal seat type is "xlocal" (also a bit of a confusing name that's still like that for backwards compatibility). The "unity" is the seat type for Unity 8 which uses Unity System Compositor to switch between sessions and not VTs.

There has never been an option in the daemon to disable user switching - it's just been left to the greeter / shell to hide those options if they're not required. lp:~robert-ancell/lightdm/disable-user-switching adds such an option.

I'm a bit confused about your custom greeter changes to avoid this - are you only talking about the case where a user ends up at the greeter because the shell allowed them to go there (which you don't want)? So this is just a safety to stop them doing a user switch if that happens?

Let me know if this branch solves your requirement.