How to run an app on a secondary monitor

Marius Gedminas marius at
Sun Mar 11 12:45:49 UTC 2012

On Sat, Mar 10, 2012 at 06:25:47PM +0200, Amichai Rotman wrote:
> I am about to participate in a computer fair at the local mall. I'd like to
> use only my netbook as my computer.
> I want to use the internal LCD for my own work and at the same time connect
> an external LCD monitor that will face the visitors, where I can run
> presentations and videos of my products.
> Cany you tell me how to set it up?

Plugin in an external monitor.  If you get a cloned display, open
Display Settings from the Power-Cog menu on the top-right corner of the
screen, and uncheck the 'Mirror Displays' box -- you'll get an extended
desktop.  Drag the apps you want to show on the external display to that
side, drag your local apps to your side.

One caveat: workspace switching in Unity will switch both displays.  If
you want your projector to always show the same stuff, you'll have to
manually select "Show this window on all workspaces" from the window
menu of each window there.

Alternatively, apt-get install gnome-shell and select a GNOME Session
from the login screen.  GNOME Shell workspace switching changes only
your primary screen; the projector will always show the same set of

(I'm assuming you're running Ubuntu 11.10, where gnome-shell is easily
installable from the standard repositories).

> I am guessing I have to set up the D-Sub as a separate X display,  but I
> have no idea how to do it...

If you do it the way I suggested, there's no complex setup necessary,
but it's possible that newly opened apps might show up on the external
screen, and that you'll have to drag them back to the internal one.  If
that's not acceptable, then hm...

You don't need to set up a separate display, it would be enough to set
up a separate X screen (:0.0 and :0.1).  Each would get its own login
screen and they would run an independent set of applications.  You could
move the mouse between screens, but you could not move windows across.

I haven't done this in *ages*.  It used to be achievable by editing an
xorg.conf file to specify multiple monitors, and a ServerLayout
configuration, and, most importantly, to turn off Xinerama.

I don't even know if modern X supports this kind of configuration any

Marius Gedminas
Every nonzero finite dimensional inner product space has an orthonormal basis.

It makes sense, when you don't think about it.
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