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I'm running 12.10 on a dell e5400 laptop and I used xrandr to get the dual monitors working that I connect through a laptop dock. I used xrandr again to switch back to the laptop display when I undocked. The problem is, after a restart, the laptop seems to want to come back up with the dual monitor configuration and the laptop screen stays blank. I can boot into single user mode but I'm not sure what to do from there to get the display settings reset. Any ideas? There's no xorg.conf file so I'm not sure where the settings are stored anymore.


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Here's what worked for me:

In a terminal, type:


You'll see various modes, which look something like this:

eDP1 connected 1440x900+0+0 (normal left inverted right x axis y axis) 30mm x 179mm
   1440x900       60.0*+   59.9  
   1360x768       59.8     60.0  
   1152x864       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
   2560x1440_30.00   29.9  

In my case, HDMI1 was the external monitor.

So, I just ran:

xrandr --delmode HDMI1 2560x1440_30.00

Now, when I plugged in the external monitor, it was as if it was the first time Ubuntu saw it.

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when trying to run xrandr from the terminal, it says "can't open display". It works in gui console, but not in the ctrl+alt+f# – Martin Melka Feb 27 '13 at 9:02
Run export DISPLAY=:0 if you get this message, "can't open display" – Jeroen Kransen Feb 20 '15 at 12:13

don't know if this is the solution for you, have you read this or this?

not sure if light-dm ( set prior to gdm by 12.10 - contrary to 12.04 ) causes this ? light-dm affects somehow startx ?

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