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Dual monitors on Ubuntu 8.04 bug July 6, 2008

Posted by claudio in Uncategorized.
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Nowadays, the GNOME screen resolution setting allows you to configure multiple screens pretty easy. It seems to work just fine. However, it’s a front-end to the X config an as such it has some problems. In my case, it allows me to clone my main monitor (is that useful to anyone?), but not to extend my desktop over both monitors.

The problem is related to the frontend not passing the errors from the underlying system (xrandr), so you don’t get any hints why it does not work. Maybe my home setup is kind of strange as I use two different resolutions (an LCD 1280×1024 connected though vga and the laptop 1024×768 screen as a second monitor), but still it shouldn’t be that uncommon. I enable the dual monitor setup when useful (gimp), but most of the time I find the different resoltion annoying. At work I use two 1680 x 1050 LCDS.

Anyway, the solution to enable a dual monitor is pretty simple.

The bug is described here in case you want to wait for (or better, contribute to) the official fix. More detailed info here.

In short, you need to edit the X config file and create a virtual desktop of the desired size. Just make the sum of the maximal size of both screen resolutions. In my case:

Monitors next to each other:

Width: 1280 and 1024 => 2304 (the desktop is extended in the width, so you need the sum)
Height: 1024 and 768 => 1024 (the desktop has the height of the biggest monitor)

One monitor below the other:

Width: 1280 and 1024 => 1280 (the desktop has the width of the biggest monitor)
Height: 1024 and 768 => 1792 (the desktop is extended in the height, so you need the sum)

Edit the X config:

sudo gedit /etc/X11/xorg.conf

Go to the Section “Screen”, then within to the SubSection “Display” (create it if not present) and add “Virtual <selected size>”:

SubSection "Display"
#Modes           "1024x768"
Virtual           1280 1792
EndSubSection

There is a catch. It’s more natural to create a virtual desktop with the screen logical next to each other, but I chose to stack them to keep the 3D hardware acceleration (compiz). Some video drivers (like my intel) disable hardware acceleration once your desktop is bigger than 2048×2048 pixels.

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Comments»

1. jmoran - July 13, 2008

don’t see what you’ve displayed as an output. i get:

Section “Screen”
Identifier “Default Screen”
Monitor “Configured Monitor”
Device “Configured Video Device”
EndSection

any suggestions? thanks.

2. claudio - July 13, 2008

Try somethig like this (adapt the values at “Virtual”):

Section “Screen”
Identifier “Default Screen”
Monitor “Configured Monitor”
Device “Configured Video Device”
SubSection “Display”
Virtual 1280 1792
EndSubSection
EndSection

3. jmoran - July 13, 2008

lost the 2nd monitor at reboot and booted to low graphics mode.

4. claudio - July 13, 2008

Make sure there is no syntax error in the xorg.conf file. I had that too.

5. jmoran - July 13, 2008

appreciate your help-this is new ground.
how do you verify syntax?

6. Slayr007 - July 15, 2008

what about installing grandr


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