How to change the default program for a specific file extension system-wise in kde or xfce?

Question

I'd like to have certain file extensions to be opened with some specific programs. What are the files the edit ? I have found in /usr/share/appplications/default.list but it doesn't work.

Answer 1

Have a look at the file $HOME/.local/share/applications/defaults.list

There is a section [Default Applications] to specify the programs for particular mime types. You can add for example:

application/x-debian-package=gdebi.desktop

The .desktop files can be found in /usr/share/applications/ or you can create your own files under $HOME/.local/share/applications/. To find out the mime type of the files, run

file --mime-type <some_file>

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Alternatively, in KDE one can accomplish the same in GUI in File Associations inside System Settings.