Re: Cannot run nvidia-settings - Error:The control display is undefined; Please run nvidia-settings
Nvidia settings looks like an X app to me so needs a graphics display window. There are numerous safe mode settings available on my installation from the menu that appears when you boot up (not the 1st boot splash menu, just use safe mode there). One of the terminal prompts offered seems to be bash running under X. You could try from there.
Also nvidia seem to use --help as an option and that may work from the prompt and give you a clue.
I to found that the one click install didn't work. Suspect it's well out of date.
I have posted a method using yast and a specific repo but only for one screen. I haven't tried adding a 2nd card that way yet but probably will at some point.
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Leap 42.2 KDE 5.26
3.6gig Xeon, 64bit SATA Raid home - Linux Raid 1
All software on a flash drive, SATA swap & Temp files,