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I've been trying to set up an external monitor for a bit, finally got it mostly working except the resolution is off. My monitor's native res is 1600x900, which I finally got to show up in xrandr:

user:~$ xrandr
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 640 x 480, current 1024 x 768, maximum 1600 x 900
default connected 1024x768+0+0 0mm x 0mm
   1024x768        0.0* 
   800x600         0.0  
   640x480         0.0  
   1600x900       59.9

However when I try to change the resolution I get the following error:

user:~$ xrandr --output default --mode 1600x900
xrandr: Failed to get size of gamma for output default
xrandr: Configure crtc 0 failed
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The crtc is a part of your graphics adapter that decides what pixels should be what color as your screen is painted on your monitor (it does all of the timing)--so this may mean that though you monitor may be able to use this mode, your graphics adapter can't. It might be helpful to know about your equipment, the contents of /var/log/Xorg.0.log, and know what you had to do to get that resolution into xrandr's display. The other 0.0 displays look strange, by the way. –  John S Gruber May 19 '12 at 3:15
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1 Answer 1

I found that problem with ATI video drivers, with deactivated driver all works.

Use

xrandr --verbose

to determine your ctrtc number? And try correct output syntax, e.g.:

xrandr --crtc CRT1 --output CRT1 --brightness 0.7

other outputs:

  • the Intel driver uses LVDS, VGA, TMDS-1 (TMDS-2, ...), TV
  • the ATI driver uses LVDS, VGA-0 (VGA-1, ...), DVI-0 (DVI-1, ...), S-video
  • the RadeonHD driver uses PANEL, VGA_1 (VGA_2, ...), DVI-I_1/digital or DVI-I_1/analog (DVI-I_2/digital or DVI-I_1/analog, ...), TV_7PIN_DIN
  • the NV driver uses LVDS, VGA0 (VGA1, ...), DVI0 (DVI1, ...), ???
  • the MGA driver uses ???, VGA (or VGA1, VGA2, ...), DVI (or DVI1, DVI2, ...), ???
  • the Nouveau driver uses LVDS, VGA-1, DVI-I-1, HDMI-1, ???
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