Suppose you create a graphics design on a Debian or Ubuntu based
operating system and point the fonts used to generic names like
sans-serif. How do you know which corresponding system font was
used? Easy, run this command:
fc-match -s sans-serif
And pick the first “branded” font name from the list. It should match the metrics of the font you used in your graphic design. Better yet, prefer to point your graphics design sources only to branded fonts so that it is easier to reproduce the original from the sources in the future. And, of course, always use only libre fonts or fonts of your own design.
20191230/DuckDuckGo ubuntu find which font is used for sans-serif
20191230/https://askubuntu.com/questions/61112/whats-the-default-serif-font-in-firefox