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Tags: display   display-resolution  
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Title: Cannot use full resolution of external display
ID: /2020/08/23/Cannot-use-full-resolution-of-external-display
Created: August 23, 2020
Upload: November 24, 2022    Layout:  post
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First you don’t need to use sudo with xrandr.

Second you need to run cvt to get the settings to pass to xrandr --newmode. For example (on my 4K TV):

cvt -v 3840 2160 56

Warning: Refresh Rate is not CVT standard (50, 60, 75 or 85Hz).
# 3840x2160 55.98 Hz (CVT) hsync: 124.95 kHz; pclk: 661.75 MHz
Modeline "3840x2160_56.00"  661.75  3840 4152 4568 5296  2160 2163 2168 2232 -hsync +vsync

Then copy the Modeline output as input for xrandr --newmode:

$ xrandr --newmode "3840x2160_56.00"  661.75  3840 4152 4568 5296  2160 2163 2168 2232 -hsync +vsync

X Error of failed request:  BadName (named color or font does not exist)
  Major opcode of failed request:  140 (RANDR)
  Minor opcode of failed request:  16 (RRCreateMode)
  Serial number of failed request:  52
  Current serial number in output stream:  52

The refresh rate is too high in this case so I reduced it to 54 Hz and repeated the process.

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