Ubuntu – Unable to change Display settings (esp “Display Scale”) with some monitors in 17.10 with Gnome Shell

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I just updated to 17.10 (Artful Ardvark), thereby making the switch to Gnome Shell. I found that when I logged in, it had set up Gnome Shell's "Display Scale" for the screen on my Lenovo ThinkPad Carbon X1 to 200% by default (leading to some weird desktop interface artifacts). I think this is because it thinks anything with ultra high res (hidpi?) should render this way. No big deal. I was able to change it to 100%, which is how I like it (crisp, small fonts). However, after that, when I tried to connect to another monitor (specifically an Apple 27' monitor), the laptop screen went back to 200%. Strangely though, when I go to try to open the Settings app to change this, the keyboard and/or screen locks up until I unplug the monitor. How do I get my monitor to run at the 100% scale when connected to an external monitor?

Best Answer

I think I may have figured this out... Should be a better answer than this though.

By going back to just the single monitor, I'm able to open settings again. If I switch the scale back to 200% (the default), I'm able to then plug the monitor in and open Displays with out anything weird happening, and change the laptop monitor scale to 100%. When I disconnect the cable again, my laptop screen goes back to 200%, but I'm able to switch it back to 100% at that point. The next time I connect that monitor, it goes back to the 100% scale I left it at, and at this point things seem hunky dory for me.

However, it appears that I have to go through this whole process every time I connect a new monitor. A bit annoying.

The bottom line here is that is seems like per monitor there is some "default scale", and when you connect a new secondary to it, it creates a new combination based on the default. But if for whatever reason it has to "change" the default going between the two, things get all snookered.

It would seem this is a bug with Gnome. Ideally this would be fixed, but at the very least having a more intelligent default monitor scale setting would do the trick. Hopefully someone has a better answer than I do about how to resolve this issues without going through this mess for each new monitor. If not, may my discovery serve useful to someone trying to hack their way out of the problem.