Every time I reinstall a Linux distribution and try to use 2 screens (my laptop screen and an external one), I have to struggle with the Xorg configuration.

As I now installed Kubuntu 10.10, I was very pleased to see that I easily can change the configuration on the KDE System settings. But my joy was only a for short time as I figured out that Kubuntu 10.10 is not able to set the resolution of my external screen correctly. The desired resolution, 1280×1024 just is not listed.

As the file /etc/X11/xorg.conf is not existing anymore, there has to be another way. After a long search I found the tips for the solution on those 2 websites: http://reustle.tumblr.com/post/1607857706/force-screen-resolutions-on-ubuntu-10-10 and http://www.jejik.com/articles/2008/10/setting_up_dual_monitors_system-wide_with_xrandr_on_debian_lenny/

The solution is to use xrandr. A simple “xrandr” in the terminal shows you the available devices and their resolutions:

Screen 0: minimum 320 x 200, current 2720 x 1024, maximum 8192 x 8192
VGA-0 connected 1280x1024+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
 1360x768       59.8
 1024x768       60.0*
 800x600        60.3     56.2
 848x480        60.0
 640x480        59.9     59.9
 680x384       119.6    119.9
 512x384       120.0
 400x300       120.6    112.7
 320x240       120.1
LVDS connected 1440x900+1280+0 (normal left inverted right x axis y axis) 303mm x 190mm
 1440x900       60.0*+   50.0
 1280x854       59.9
 1280x800       59.8
 1280x720       59.9
 1152x768       59.8
 1024x768       60.0     59.9
 800x600        60.3     59.9
 848x480        59.7
 720x480        59.7
 640x480        60.0     59.4
DVI-0 disconnected (normal left inverted right x axis y axis)

As you can see, VGA-0 does not have the correct resolution of 1280×1024.
This can now be added with those commands:

xrandr --newmode "1280x1024"  109.00  1280 1368 1496 1712  1024 1027 1034 1063 -hsync +vsync
xrandr --addmode VGA-0 "1280x1024"

To get the values for the first line, you can use this command:

cvt 1280 1024 60

Which should return something like this:

# 1280x1024 59.89 Hz (CVT 1.31M4) hsync: 63.67 kHz; pclk: 109.00 MHz
Modeline "1280x1024_60.00"  109.00  1280 1368 1496 1712  1024 1027 1034 1063 -hsync +vsync

Just drop the first line and the “Modeline”. Also I renamed the label from “1280x1024_60.00″ to “1280×1024″.

Now you can tell the X server to use the new resolution:

xrandr --output VGA-0 --mode 1280x1024

I also had to do it for the internal screen:

xrandr --output LVDS --mode 1440x900

Now we can change to the dual screen:

xrandr --output VGA-0 --left-of LVDS

Sadly it always takes my external screen as primary. According to some websites, this can be solved when you swap the two “mode” commands listed above, how ever it did not work for me. After some more research I found this working solution to set the internal screen as primary:

xrandr --output LVDS --primary

Sadly those changes get lost every time you restart the X server.
I did not find a way to make them permanent, so I have to execute those commands after every restart. To make my life easier, I put them into a script which gets executed automatically after I log in.

As I not always have an external screen, I made the script detecting if I have an external screen is connected. If not, it switches the (not connected) external screen off.  On http://www.jejik.com/articles/2008/10/setting_up_dual_monitors_system-wide_with_xrandr_on_debian_lenny/ you can find an even better script. Mines looks like that:

#!/bin/sh
xrandr | grep VGA | grep " connected "
if [ $? -eq 0 ]; then
 # External monitor is connected
 xrandr --newmode "1280x1024"  109.00  1280 1368 1496 1712  1024 1027 1034 1063 -hsync +vsync
 xrandr --addmode VGA-0 "1280x1024"

 xrandr --output LVDS --mode 1440x900 --output VGA-0 --mode 1280x1024

 xrandr --output VGA-0 --left-of LVDS
 xrandr --output LVDS --primary

else
 # External monitor is not connected
 xrandr --output LVDS --mode 1440x900 --output VGA-0 --off
fi

Also when ever I plug in/out the external screen, I just run this script and my screens get set up as desired.