Ubuntu – How to list connected displays using the command line

This behaviour is by design. The GNOME designers decided this was the best thing to do, not taking their actual users into account.

Luckily the behaviour can be reverted. You can use Gnome Tweaks or execute the following in the terminal, re-login and you're all set:

gsettings set org.gnome.shell.overrides workspaces-only-on-primary false

or using this on older systems:

gconftool-2 --set /desktop/gnome/shell/windows/workspaces_only_on_primary false --type bool

You probably want to have panels and workspace preview on all monitors too: How to have both monitors in the workspace preview for Gnome Shell?

You have to make two scrips to achieve your goal.

one to switch both external displays on and turn off your laptop display.

and the other to revert the change made by script one.

So create script1.sh and make it executable with following contents.

#!/bin/bash
    xrandr --output LVDS-1 --off  
    xrandr --output VGA-1 --mode 1920x1080 --auto
xrandr --output HDMI-1 --mode 1920x1080 --auto

and script2.sh with following contents and make this too executable.

#!/bin/bash
xrandr --output VGA-1 --off
xrandr --output HDMI-1 --off
xrandr --output LVDS-1 --mode 1366x768 --auto

You can run the scipt1.sh after connecting the external displays and you have to run the script2.sh before removing the external displays.

Note that the above method will mirror your screen to two separate screens at the same time. And if you need a separate screen rather than mirroring, you can use either --left-of or --right-of option and provide device names accordingly.

And also you can check if your hardware supports three displays at the same time by turning on the laptop display along with the two monitors.