Dual monitor with different resolutions
The answer depends on your specific hardware. DPI won't be directly configurable using the standard Kubuntu display configuration tool, but if you try to lower the resolution on a monitor with a better DPI, you can get closer to the effect you want. You can also try to generate a file xorg.conf
and customize it, but you won't go much further than using the display tool.
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DPI setting is incomplete in KDE4. AFAIK there is no default tool for specifying DPI with every monitor behavior, only global. Workspaces5 is supposed to perform better on hi-DPI settings, but it's not ready for the public just yet. However, I'm not sure if this is what you are asking for.
There might be a way to make the DPI for each monitor in xorg.conf (which you don't have yet, despite using X of course), but that might break other things. You can try to force a specific DPI that works well for both screens under System Settings → App Appearance →.
As for the resolution setting, you can adjust it under the standard "Display Configuration" or "Size and Orientation" dialogs under "System Preferences" → "Display and Monitor". On my system, it automatically pops up when a new screen is detected, but this may depend on HW and SW version.
I've never had any problems with external screens, but it depends on the resolution used. My laptop is 1280x800 and the highest resolution external screen I have used is 1920x1080. What permissions are you using?
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