Workaround for the Ubuntu problem with KVM switches

August 26, 2009

It seems that Ubuntu not only Karmic (9.10), but also older versions have a problem with KVM (Keyboard, Video, Mouse) switches. To be exact the problem is the auto-detection of the capabilities of the monitor. If you connect the monitor directly to the computer everything works, if you use a KVM switch you get only 800×600 as the maximum resolution.

The workaround is to tell the xserver the Horizsync and Vertrefresh the monitor really supports. With older Ubuntu versions you could just add following lines (for a 1280×1024 LCD) to your /etc/X11/xorg.conf in the monitor section:

Section "Monitor"
        .....
        Option          "DPMS"
	Horizsync 31.5-64.0
	Vertrefresh 56.0 - 65.0
        .....
EndSection

But starting with Karmic Ubuntu has no /etc/X11/xorg.conf file by default anymore. So what we need is a complete minimal xorg.conf file so we can include our 3 lines, but we don’t want to mess anything else up. This is the minimal config I came up with.

Section "InputDevice"
	Identifier	"Generic Keyboard"
	Driver		"kbd"
	Option		"XkbRules"	"xorg"
	Option		"XkbModel"	"pc105"
	Option		"XkbLayout"	"de"
	Option		"XkbVariant"	"nodeadkeys"
EndSection

Section "InputDevice"
	Identifier	"Configured Mouse"
	Driver		"mouse"
EndSection

Section "Device"
	Identifier	"Configured Video Device"
EndSection

Section "Monitor"
	Identifier	"Configured Monitor"
        Option          "DPMS"
	Horizsync 31.5-64.0
	Vertrefresh 56.0 - 65.0
EndSection

Section "Screen"
	Identifier	"Default Screen"
	Monitor		"Configured Monitor"
	Device		"Configured Video Device"
        SubSection "Display"
                Depth           24
                Modes           "1280x1024" "1024x768"
        EndSubSection
EndSection

Section "ServerLayout"
        Identifier      "Default Layout"
        Screen          "Default Screen"
        InputDevice     "Generic Keyboard"
        InputDevice     "Configured Mouse"
EndSection

Except the Keyboard stuff the should be nothing thats not minimal. Maybe it is also possible to remove some lines there, but I didn’t test it. I was happy that it worked this way . If you’ve an even more minimal config write a comment please!

1 Comment »

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1. only the device, monitor and screen sections are required as far as i can tell. it works fine on my box without the others.

   Comment by dan — November 4, 2009 #

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