How to change resolution that doesn't exists on display settings on Linux

Sometimes we need to change the resolution of our monitor, but the resolution doesn't show up on the xfce4-display-settings, what should we do? First you'll need a terminal or command prompt, then type cvt or gtf command with your desired resolution, for example:

cvt 1920 1080 

it would show something like this:

# 1920x1080 59.96 Hz (CVT 2.07M9) hsync: 67.16 kHz; pclk: 173.00 MHz Modeline "1920x1080_60.00" 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync

now, you should add it using xrandr command:

xrandr --newmode "1920x1080"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync

now, assign it the desired display port from the graphics card, first let see our graphic card available ports, type xrandr again without parameter, it would show something like this:

Screen 0: minimum 8 x 8, current 1600 x 1200, maximum 32767 x 32767
VGA1 connected primary 1600x1200+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
   1024x768      70.07 +  85.00    75.08    60.00 
   1600x1200     60.00* 
   1280x1024     85.02    75.02 
   1440x900      59.89
   1280x960      85.00
   1280x800      59.81
   1152x864      75.00 
   1024x768      86.96 
   832x624       74.55
   800x600       85.06    72.19    75.00    60.32    56.25 
   640x480       85.01    75.00    72.81    66.67    60.00
   720x400       87.85    70.08
HDMI1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)
  1920x1080 (0x2ee) 173.000MHz
    h: width  1920 start 2048 end 2248 total 2576 skew 0 clock  67.16KHz
    v: height 1080 start 1083 end 1088 total 1120 clock  59.96Hz

Now we know that we have 3 ports: VGA1, HDMI1 and VIRTUAL1, of course the current monitor was plugged into VGA1 because it shows "connected", now we could assign using this command:

xrandr --addmode VGA1 1920x1080 

and set the display resolution using this command:

xrandr --output VGA1 --mode 1920x1080

Voila, now your resolution changed!

Note: if you're using VGA Video Splitter, make sure that the monitor plugged into the first port, so it would send correct EDID.