I can no longer change screen resolutions using
xrandr. I recently put a GeForce GTX 1050 Ti card in my machine, which I suspect is the source of the problem.
I have it connected "semi-headless", meaning it's connected via DVI-D to an ancient 5:4 square monitor, and via remote control (NoMachine) with an HDMI cable and a dummy adapter. I've used this setup before, and it works fine.
Running xrandr gives a full dump of all available modes, but I can't issue a command to change the resolution.
$ xrandr --display HDMI-1 --output 1680x1050 Can't open display HDMI-1
This exact syntax has worked for a long time. Is it related to the new card? I'm using the proprietary Nvidia drivers, but I have the same problem with the "Oibaf" open-source drivers.
Some hint I came across was that I need an Xorg.conf file for this to work right. I don't have one on Kubuntu 17.10. I've got xorg.conf.d/ instead and a directory of modules.
Can anyone help? Each time I remote-connect, I have to reset the resolution to match my laptop. I spent a ton of time the last few days learning to code KDE Plasma 5 plasmoids just so I could have a handy xrandr drop-down tool. But if it won't access the display... argh.