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I run Ubuntu 18 on a PC connected to a 3440x1440 display. It is connected with a DisplayPort to HDMI adapter and a modern HDMI cable. The highest resolution available in the display settings is 1920x1080.

I tried using xrandr to force it (at both 60 and 50 hz).

$ xrandr --newmode "3440x1440_50.00"  344.00  3440 3672 4040 4640  1440 1443 1453 1484 -hsync +vsync
$ xrandr --addmode HDMI-1 3440x1440_50.00
$ xrandr --output HDMI-1 --crtc 0 --mode 3440x1440_50.00

But I get an error.

xrandr: Configure crtc 0 failed

I know that the adapter and cable can support a signal at this resolution, because if I plug the adapter into my Windows 10 machine, it uses the native resolution automatically.

I have also observed that the Ubuntu machine can output 3440x1440 over DisplayPort automatically. I would use the DisplayPort output, but unfortunately the monitor only has one DisplayPort input. I would swap the connections since the HDMI signal works from Windows, but it does so at a lower framerate, which doesn't work for my purposes.

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  • Can you clarify your whole setup? I'm confused because you say you are using DisplayPort to HDMI, but then you say you aren't using the DisplayPort output. Then you say you don't want to use the HDMI input, but again, the cable you have indicated is DisplayPort to HDMI. Do you have more than one device connected to the monitor? What's the reason you can't use native DisplayPort to DisplayPort? Avoiding an adapter should be high priority IMO
    – Nmath
    May 28, 2020 at 19:13
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    Try 30 Hz refresh and if that works bump to 45 Hz, etc until you find the highest refresh rate that works. Not all adapters are created equal. My original only worked to 30Hz so I bought one rated for 60 Hz at 4K but the best I got from it was 54 Hz May 29, 2020 at 12:34
  • @Nmath I can't use the native DP to DP because the monitor only has one DP input, but I use it with two different machines. The setup is like this: Ubuntu Machine DP output -> adapter -> HDMI cable -> Monitor HDMI input.
    – tnunamak
    May 29, 2020 at 22:31
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    @tnunamak Good to hear. I'll post an answer based on my comment. May 30, 2020 at 0:16
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    @Nmath Unfortunately with USB-C Thunderbolt III (40 GB/s) there is no choice but to use an adapter. The nVidia GTX 970M HDMI port is already plugged into one TV and the Display Port to HDMI adapter is the only option for a second TV. The 17" laptop display whilst nice, doesn't provide the square footage needed for a productive living room. I think these USB-C adapters are really cool and I wouldn't be so quick to broadly dismiss adapters in general. Yes there are different qualities and you need to shop carefully for Linux. May 30, 2020 at 0:26

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Try 30 Hz refresh and if that works bump to 45 Hz, etc until you find the highest refresh rate that works.

Not all adapters are created equal. My original only worked fine at 1920x1080 at 60Hz. When I upgraded to a 4K TV it only worked at 30Hz. So I bought a new adapter rated for 60 Hz at 4K but the best I got from it was 54 Hz.

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