Theoretically, display server should be able to derive a proper DPI setting from EDID, but in reality this could fail at times. (eg. OS running in a VM.) In order to have things readable on HiDPI displays, we may have to adjust scaling factor manually.

GNOME

In terminal, run

gsettings set org.gnome.desktop.interface scaling-factor 2

To check your setting, dump dconf setting with

dconf dump /

or simply

dconf read /org/gnome/desktop/interface/scaling-factor

There should be something like

scaling-factor=uint32 2

GDM

For Debian-based distros:

1. Edit /etc/gdm3/greeter.dconf-defaults as root
2. Add

   [org/gnome/desktop/interface]
   scaling-factor=uint32 2

3. Save and close the editor
4. Finally, run as root:

   dpkg-reconfigure gdm3

For other distros, check links below. 😬

References

• GNOME – HiDPI – ArchWiki
• gsettings – GIO Reference Manual
• Customizing the GDM appearance – GDM – Debian Wiki
• Customizing the Login Screen – Desktop Migration and Administration Guide – Red Hat
• DConf configuration – GDM – ArchWiki