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

To check your setting, dump dconf setting with

or simply

There should be something like

GDM

For Debian-based distros:

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