while in X Windows one can press Ctrl+Alt+F1 (or F2 .. F6 or so) and X is disconnected from the physical console and (one of) the kernel's text console(s) become(s) active. what i would like to know is how is the state that X is in is referred to. what terminology would this be referred to in X documentation?

it is possible to run 2 or more instances of X Windows at the same time. many years ago i would run 3 instances of X Windows in parallel on F10, F11, and F12. i would always switch between them with Ctrl+Alt+F10 (or Ctrl+Alt+F11 or Ctrl+Alt+F12). the instance of X i was switching away from could, in theory, see that i was switching away. today, Xubuntu (and perhaps also Ubuntu) runs LightDM which can carry out the switch without any press of the keyboard. both instances of X know it happens since they both need to act to carry out the details of making the switch happen. this can be done with the command "dm-tool switch-to-user $username". i'd like to know how the X servers get to know this. i assume it is some kind of interrupt or signal but i don't know a way to trap or trace this.

also, it seems the Firefox web browser gets to know this, too. it used to no act on it,such as when playing a YouTube video which would just keep on playing with no one watching. recently, it was changed to pause the video. i would like to know if there is a setting that can have it keep on playing without pausing when X does this.

when i am running ffmpeg to record the screen and i switch to viewing another user (which is always running a different X Windows server) the recording keeps running but all that is recorded is a black screen. maybe capturing the screen uses a hardware buffer to do that. so i may need to switch to using VNC to switch around with each user running an X-over-VNC server and me running a VNC client which will also do the switching. as far as i am aware, sound has not been added to the VNC protocol.