I got a problem using Xubuntu 14.04 LTS while connecting it to the HDMI port from a Samsung LN40R81. Straight to the point, the resolution is lower than the required (1366 x 768). This resolution option does not appear.
Besides, there is no xorg.conf file to make changes. And I have arandr installed, by the way.
My xrandr output on console goes like this:
Screen 0: minimum 320 x 200, current 1366 x 768, maximum 32767 x 32767 LVDS1 connected 1366x768+0+0 (normal left inverted right x axis y axis) 309mm x 174mm 1366x768 60.0*+ 1360x768 59.8 60.0 1024x768 60.0 800x600 60.3 56.2 640x480 59.9 VGA1 disconnected (normal left inverted right x axis y axis) 1656x900_60.00 59.9 HDMI1 connected 1280x720+0+0 (normal left inverted right x axis y axis) 160mm x 90mm 1280x720 60.0*+ 50.0 59.9 1920x1080i 60.1 50.0 60.0 720x576 50.0 720x480 60.0 59.9 640x480 60.0 59.9 DP1 disconnected (normal left inverted right x axis y axis) VIRTUAL1 disconnected (normal left inverted right x axis y axis) 1368x768_60.00 (0xf2) 85.9MHz h: width 1368 start 1440 end 1584 total 1800 skew 0 clock 47.7KHz v: height 768 start 769 end 772 total 795 clock 60.0Hz
I just need to add the 1366x768 resolution, or at least the 1360x768, on which will make least difference for its usage.
EDIT Trying Volker Siegel's links, now appears this:
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: 36 Current serial number in output stream: 36
LAST EDIT (TEMPORARY ANSWER)
Well, I checked a little more about my screen and found a temporary solution. Why? It only works using extended screen, not mirroring them. When I mirror them, I cannot change both screen resolutions to the point I could observe 90% of all screen content on both monitors. So now I am using extended screen mode, because I can change both resolutions apart.
Still, if somebody could help me to add screen resolutions to my Xubuntu (or explain me why I can't), it will be fully apreciated.