Default applications for each file type are set in a text file /usr/share/applications/defaults.list . In the file, an application is assigned to each file type as a default application as text/plain=gedit.desktop The above line means that gedit is used to open a plain text file as a default application. Editing the corresponding lines in the defaults.list therefore enables to change default applications.
We should make sure that a .desktop file of application X exists in same directory like /usr/share/applications/X.desktopOtherwise, we need to make a .desktop file before changing the defaults.list.
I changed:
