Can't use startx on another tty

mohammadbagheri2010; Hey ..

Be aware, we may be in for a long hard tough fight now-a-days to make this happen.
See: https://ubuntuforums.org/showthread.php?t=2330506

Which indicates that in 16.04 (systemd) will be a real challenge.
Which raises the question of which release we are working with ,, will make a big big difference.
To know what you have for the DE and the Display manager:

echo $DESKTOP_SESSION " " $XDG_CURRENT_DESKTOP
cat  /etc/X11/default-display-manager