Associate all audio and video files to VLC instead of Totem media player (Movie Player)
Video files: .avi .mp4 .mpg .ogv .ogm .mkv .wmv etc.
Audo files: .mp3 .ogg .flac .wav .wma etc.
Open defaults.list with gedit:
gksudo gedit /usr/share/applications/defaults.list
And replace all occurences of totem with banshee/rythmbox/vlc or the media player of your choice.
(Search → Replace → Replace All) (=totem.desktop => =vlc.desktop)
Save the modified file, and you're done! Change are effective immediately.
Associate all office documents to LibreOffice instead of OpenOffice.org or Abiword
Office files: .odt .ods. .doc .docx .xls .xlsx etc.
Open defaults.list with gedit:
gksudo gedit /usr/share/applications/defaults.list
And replace all occurences of "openoffice.org" with "libreoffice".
(Search → Replace → Replace All)
Finally, save the file. No need to restart, you're all set!
Ubuntu's case
For an obscure reason, changing the file associations directly in the defaults.list doesn't seem to work Ubuntu 10.10 "Maverick Meerkat". Nevertheless, importing information to the the mimeapps.list works.
The file associations for each user are stored in:
~/.local/share/applications/mimeapps.list
In Ubuntu 10.10 "Maverick Meerkat" (and probably 10.04 "Lucid Lynx"), this file is almost empty. Let's import informations from
/usr/share/applications/defaults.list
Display all the video MIME types associations with this command:
cat /usr/share/applications/defaults.list | grep video
Append all the lines containing video types to the local file:
cat /usr/share/applications/defaults.list | grep video >> ~/.local/share/applications/mimeapps.list
Open defaults.list with gedit:
gedit ~/.local/share/applications/mimeapps.list
And replace all occurences of totem with vlc (Search → Replace...) Proceed similarly for audio files if needed.
来源： http://www.libre-software.net/change-the-default-application-linux-mint-ubuntu