I’ve been using this Samsung 4K screen for 3 years. I never adjusted any of the parameters for making things larger. I just got used to the small fonts, and blew things up by application when I needed to.

I’ve been doing some reading in anticipation of getting a new laptop maybe with hidpi. Learned stuff about changing resolution.

With Gnome-Tweak tool->Windows->HIDPI Window scaling, can blow up everything in Gnome. Can only have integer values, so with 2, I can double the size. But after several years of smaller sizes I don’t really like this. Might need it on the laptop though.

With Firefox and Thunderbird, use config editor and find layout.css.devPixelsPerPx. This can have non integer values and 1.5 in Thunderbird is better for me. For Firefox I currently have it set at 1.3.

Can also use xrandr to change various properties. Use just

xrandr

to see names of monitors, and use

xrandr --output HDMI-1 --scale 0.9x0.9

or

xrandr --output HDMI-1 --dpi xxx

There is good xrandr info at https://wiki.archlinux.org/index.php/xrandr.

Update:

After I got the new Hidpi laptop, I had to learn a lot more. Here are the settings, all available with gsettings get/set.

gsettings get org.gnome.desktop.interface.scaling-factor, which is same as gnome-tweak-tool->Windows->HiDpi Windows Scaling

(2 on laptop, 1 on oregano)

gsettings get org.gnome.desktop.interface.text-scaling-factor, which is same as gnome-tweak-tool->Fonts->Scaling Factor

1.0 on both

gsettings get org.gnome.desktop.interface cursor-size

24

gsettings get com.ubuntu.user-interface scale-factor

{‘DP-0’ : 16} on the laptop, makes the window panel text more closely match the drop down text.

gsettings get org.gnome.settings-daemon.plugins.xsettings overrides

{‘Gdk/WindowScalingFactor’ : <2>}

This ended up being the most important one of all, and hardest to find anything about. This seems to affect thing built with gtk++ which is a lot of stuff. The others – the org.gnome ones affect the gnome stuff, but not the apps. This one affects all the apps built with gtk (qt too?? I don’t know).

Found another article which wanted to also set in the same key (in addition). Note 161226 is the dpi (157.35 for the Samsung U28D590D) in “1024’s of an inch”, ie times 1024. The laptop is 3840×2160 but on a screen which is actually only 13.5″ wide,  so the DPI comes out at around 284 and in 1024’s is 286720.

{‘Gdk/WindowScalingFactor’ : <2>, ‘Xft/DPI’: <161126>}

or, a different one. The comments I’ve seen in code suggest this has to do with figuring out what apps are not scaled, and using this for them.

{‘Gdk/WindowScalingFactor’ : <2>, ‘Gdk/UnscaledDPI’: <161126>}

Setting the former on Oregano made things way too big. The latter didn’t seem to do anything. On the laptop – it was the reverse. The former didn’t do anything, and the latter made things huge. I also tried half the pixel density on the laptop, which was better. But it still didn’t help eclipse.

The big problem is java apps. Java stuff built with swt doesn’t react to the gtk setting.