“Unknown Display” on Centos 7 (Desktop)

Linux

In a continued bid to build a desktop Linux machine, I was working on getting the three monitors working. One of the monitors uses the onboard graphics, the other two are plugged into a PCI-E riser card. The issue was that the monitor type is not detected by the onboard graphics, so reports the incorrect resolution back. Changing this was proving very difficult. I’m using GNOME on Centos 7 desktop.

To fix I did the following to get the correct modeline I needed:

cvt 1440 900 60

Modeline “1440x900_60.00” 106.50 1440 1528 1672 1904 900 903 909 934 -hsync +vsync

All my monitors will be running at 1440x900_60.00.

Now I ran an: xrandr to get the list of all the monitor/adapter names. In my case these were VGA-1-1 (the unknown display, on the motherboard graphics), VGA-2 and DVI-I-1 (the latter two were on the riser PCI-E card).

Finally I created a file called: /etc/X11/xorg.conf.d/10-monitor.conf and adding the following contents:

Section “Monitor”

Identifier “VGA-1-1”

Modeline “1440x900_60.00” 106.50 1440 1528 1672 1904 900 903 909 934 -hsync +vsync

Option “PreferredMode” “1440x900_60.00”

EndSection

Section “Monitor”

Identifier “VGA-2”

Modeline “1440x900_60.00” 106.50 1440 1528 1672 1904 900 903 909 934 -hsync +vsync

Option “PreferredMode” “1440x900_60.00”

EndSection

Section “Monitor”

Identifier “DVI-I-1”

Modeline “1440x900_60.00” 106.50 1440 1528 1672 1904 900 903 909 934 -hsync +vsync

Option “PreferredMode” “1440x900_60.00”

EndSection

Once this was done I rebooted, but the third monitor was not using the correct resolution.

Using “Settings”->”Display” I set the problem third monitor (VGA-1-1) to 1440×900 which was now an available option and ensured the monitors were in the correct positions.

One more reboot and all was then in order.

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