Ubuntu (and Linux in general) has a lot of things going for it.  Running dual monitors, however, is not one of them.  Speaking from personal experience, it is easy to waste several hours trying to get your dual monitor setup to work correctly.  After playing around with various solutions, I have finally found one that works – at least for me.

I am running Ubuntu 10.04 and have two Dell monitors plugged into my computer’s add-on graphics card.  The main monitor (1920×1080) uses the DVI connection while the secondary monitor (1440×900) uses the VGA connection.  For whatever reason, the built-in monitor functionality under System->Preferences->Monitors kept crashing my monitors whenever I tried to make any changes.  So, instead of using the GUI to set up my monitors, I resorted to the command line.

It turns out that the xrandr command is actually quite easy to use.  I referenced my information from this site, but posted a few of the most useful commands below. These commands are all entered in the terminal.

To see the current monitor configuration type xrandr. An example output is shown below:

mark@markacl:~$ xrandr
Screen 0: minimum 320 x 200, current 3360 x 1080, maximum 4096 x 4096
VGA-0 connected 1440x900+1920+180 (normal left inverted right x axis y axis) 408mm x 255mm
   1440x900       59.9 +   75.0*
   1280x1024      75.0     60.0
   1280x800       59.8
   1152x864       75.0
   1024x768       75.1     70.1     60.0
   832x624        74.6
   800x600        72.2     75.0     60.3     56.2
   640x480        72.8     75.0     66.7     60.0
   720x400        70.1
DVI-0 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 531mm x 298mm
   1920x1080      60.0*+
   1280x1024      75.0     60.0
   1152x864       75.0
   1024x768       75.1     60.0
   800x600        75.0     60.3
   640x480        75.0     60.0
   720x400        70.1
S-video disconnected (normal left inverted right x axis y axis)

If the primary screen (the one with the links on top and such) defaults to the wrong monitor, you can change it by using the --primary command. For instance, if you wanted your VGA output to be primary, type

xrandr --ouput VGA-0 --primary

To change the position of your two screens with respect to each other use the --left-of or --right-of commands. For me to get my VGA monitor on the right of my DVI, I used

xrandr --output VGA-0 --right-of DVI-0

Also, you can change the position of the monitors to get just the right orientation with respect to each other. To get my second monitor to line up with the bottom of my first monitor, I used

xrandr --output VGA-0 --pos 1920x180

The position function relates to the upper left pixel of the monitor. I wanted my second monitor 1920 pixels left of my first (the width of the first) and 180 pixels lower (1080 – 900).

Good luck!