Initially you asked for "console in full screen from desktop", and you added later you want it from linux.
It's still not clear what you're looking for. You can press C-M-F1 (meaning holding down Ctrl and Alt, press the F1 key), C-M-F1 etc to switch between virtual (text-only, full screen) consoles. This doesn't terminate the X11 window system (which you may be referring to as "desktop"?); C-M-F7 will return you to it.
(A) I'm not sure how this relates to /dev/console (if that's what you're looking for); it acts like /dev/console dynamically gets redirected to whatever virtual console I'm looking at (/dev/tty1, /dev/tty2, etc.).
(B) This has nothing to do with single user mode (a much bigger hammer) about which you asked, too.
Why do you need a full screen console? What are you trying to do?