How does Unity work in multi-monitor configurations?

Unity in 10.10 appeared to be focused around single monitor configurations with a single tasking workflow. This works quite well on a netbook which has limited screen real estate.

How does the present version of Unity scale up to include multi-monitor and multi-tasking workflows?

For 10.10 multi monitor support was rudimentary, as that was focused on netbooks -- if you were giving a presentation and you ran Unity we didn't want the top panel overlaid on your presentation.

For 11.04 and 11.10 the multimonitor support is much better. I'll talk about how my setup works with Nvidia, but I don't have the hardware to comment on ATI and Intel support so hopefully someone will post seperate answers for those.

For 12.04 and 12.10 there is a specification for how to improve multi monitor support in the desktop.

Nvidia Twinview

Each monitor gets a panel with the window controls, the application menu, and then the indicators. When the windows are maximized each window gets integrated into the top panel of each screen. The indicators are cloned so that you're never too far from the system menu.

When the windows are unmaximized the application menu for that app will be displayed on whichever panel the application is on so that you don't have the menu all the way on another screen:

ATI

Using the open source ATI driver with RandR (you setup from Monitor Preferences, see screenshot) then the same result is achieved as with Nvidia Twinview.

Known Issues:

Here is a list of possible combinations of multi monitor setups and their results:

• http://people.canonical.com/~bryce/ExternalMonitor/results.html

There are some bugs (other than the first, they are generally small aesthetic details):

• Bug #742544: For users with the secondary monitor on the LEFT of the main monitor, the launcher displays in the wrong place and similarly regarding [the main panel's position, Bug #757652]
• Bug #769458: Desktop background not correctly rendered on startup
• Bug #742020: Indicators being shown as selected on both screens
• Bug #743621: Occasional problems with applications that run in fullscreen

There's still the potential to improve support further, for example the suggestion in Bug #755357 to allow two global menus to be active at the same time.

See also What's the right terminology for Unity's UI elements?

The biggest problem that I had with Unity was that it correctly identified my right monitor as the primary one and displayed the launcher on the left side of that monitor.

This caused the scenario where I could not easily invoke the launcher as moving the mouse to the left causes it to switch over to the left monitor. To show the launcher I had to either press Super (Win key) or move my mouse to the Ubuntu icon on the top panel and then slowly move to the left.

I briefly looked for a setting that would move the launcher to the right side of the screen, but did not find any. Which lead me to revert back to Gnome "classic" as it was impossible for me to use Unity with its current multi monitor support.