Filetype associations in Linux

Question

I'm curious how file association management is implemented in Linux. Where is the related information stored? How do I modify it (I'm interested in non-KDE-based ways; I know there's a system configuration page for that in KDE)?

Links to corresponding articles/documentation will be appreciated :)

Answer 1

Most desktop environments use Freedesktop.org MIME Actions spec. Every program has a .desktop file in /usr/share/applications and/or ~/.local/share/applications, providing information about the program and the MIME types it accepts. User's own preferences are kept in ~/.local/share/applications/defaults.list.

URI schemes, such as http: or mailto:, are simply listed as special x-scheme-handler/scheme MIME types. (Older programs may still be using GNOME- or KDE-specific URI scheme databases, though.)

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Some "traditional" mail programs, such as Alpine or Mutt, still use the older ~/.mailcap file for determining the best tool to view attachments with. This is partially because they are purely terminal-based, and require different mechanisms.

Answer 2

You can look at the manual (and the actual shell script) for xdg-open. It does check if you are using KDE, Gnome, lxde, and passes the file on to kde-open and so on. If you aren't running any of those, it looks them up using xdg-mime. You can look up information on how this work at freedesktop.