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I installed Debian 9 and my AMD gateway with 2 HDMI outputs. The gnome 3.22.2 desktop only showed up on 1 monitor. Followed instruction on: https://wiki.debian.org/AtiHowTo to install the video drivers. Then used a randr command from the terminal to make the 2nd monitor available in the gnome-control-panel. My extended desktop works perfectly!

Video Contgrollers: (from $ lspci)
01:05.0   [AMD/ATI] RS780 [Radeon HD 3200]
02:00.0   [AMD/ATI] Redwood PRO [Radeon HD 5550/5570/5630/6510/6610/7570]

To activate the 2nd monitor:

# xrandr --setprovideroutputsource 1 0

Then the 2nd monitor shows up in the gnome-control-panel so I can setup the extended desktop.

Problem: Every time I boot-up Debian,the desktop is only on the 1st monitor using the RS780 card.

Questions:

  1. How do I configure the system to automatically show an extended desktop on both monitors?
  2. I don't have a /etc/X11/xorg.conf; do I need one?
2

xrandr commands solved the problem.
$ xrandr
// Returns the connected video output names: HDMI-0 & HDMI-1-1.
// Then I put these 2 cmds in a bash script:

xrandr --auto --setprovideroutputsource 1 0 --auto

xrandr --output HDMI-1-1 --auto --right-of HDMI-0

  • Worked like Black Magic ;) I have one NVIDIA GTX 650 Video Card and using the motherboard Intel Based Graphics Card, I have all 3 monitors working with this magic command, it would be great if you could put on more details. Thanks for sharing – ximbal Jan 27 at 19:51
1

You should edit xorg.conf, so that you activate both card, and you give the right position. A xorg.conf-less works for common cases, but edge cases are not yet well supported. Consider that often people doesn't want to activate one graphic card (e.g. the one in CPU) when there is a better card in the system. And in any case, the xorg has no way to know which monitor is left (or above) the other.

Naturally you can also use other methods, like telling gnome to automatically execute a script that call randr, but I find it less convenient.

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