There was a time, back in the day, when having two screens on a computer was the sole privilege of advanced workstations used by graphics studios and designers. However, those days are long gone and now almost anyone can add a second (or even third) monitor to their PC, even humble Linux users!
To add a second monitor, you need a second video output. This is achieved in one of two ways. First, many video cards on sale today come with two or even three video outputs. Depending on the make, model and price, you can find cards with a variety of video output configurations, including a standard 15-pin VGA output plus a DVI output, or two DVI outputs, or a DVI and a HDMI or even VGA, DVI and HDMI. The other way of getting two video outputs is to use two video cards. For example, many motherboards have on-board video, and on some models, if you add a 3rd party video card (via the PCI Express slot), the on-board video can be re-activated in the BIOS as a secondary video output. In fact, using this trick and a video card with two outputs, it is possible to support three monitors!
Before looking at how to configure Ubuntu Linux with multiple monitors, it is worth looking at the compatibility issues between VGA, DVI and HDMI. In a nutshell, VGA only carries analogue signals. DVI can carry both analogue (as long as it has the four extra pins around the flat blades on the connector) and digital. HDMI is a digital only system. The second monitor you connect needs to have the corresponding connectors. Because DVI can carry both analogue and digital signals, it means that a VGA output can be connected to a DVI monitor using an inexpensive converter, but a VGA output can not be connected to an HDMI port (or vice versa) without a very expensive analogue to digital converter.
Connect your second monitor to your Ubuntu PC and boot it. It is likely that Ubuntu will make a good attempt to configure the second monitor automatically. However, it has no way of knowing if your second monitor is to the left or right of your main display. To configure the second monitor, go to “System Settings -> Displays”.
The top part of the configuration window will show you how many monitors Ubuntu has detected along with their names. You can click on any of the monitors and move them. So if your secondary monitor is on the other side, click to grab the monitor and move it. You can also place the secondary monitor above or below the primary monitor.
Below the monitor positioning, there are several options that are applied on a per monitor basis. To set the screen resolution for any given monitor, click on that monitor in the top section, and then select the resolution from the drop down list.
The Ubuntu launcher can be configured to appear on all monitors (the default) or just on one of them. Depending on how you use your system, removing the launcher from the second monitor can be useful, especially if the secondary monitor is to the right of your primary monitor and you want applications to extend over both monitors. However, unless you have ultra thin bezels on your monitors, this isn’t likely to be practical!
It is also possible to mirror the displays rather than extending the desktop over both monitors. This is useful for giving demonstrations or in other situations where you aren’t looking at the second monitor but rather it is being watched by a 3rd party. To enable mirroring, just tick the “Mirror displays” checkbox.
Multiple monitor support should work out-of-the-box with Ubuntu, but if you do have any questions please ask them in the comments section below and we will see if we can help.