gksu gedit /etc/mailcap

application/pdf; evince '%s'; test=test -n "$DISPLAY"; nametemplate=%s.pdf
application/x-pdf; evince '%s'; test=test -n "$DISPLAY"; nametemplate=%s.pdf
application/x-bzpdf; evince '%s'; test=test -n "$DISPLAY"; nametemplate=%s.pdf.bz2
application/x-gzpdf; evince '%s'; test=test -n "$DISPLAY"; nametemplate=%s.pdf.gz

xdg-mime query filetype foo.pdf

xdg-mime default evince.desktop application/pdf

/usr/share/applications/defaults.list
/usr/share/applications/mimeinfo.cache
~/.local/share/applications/
~/.gnome/share/apps/

xdg-open

Exec=exo-open --launch FileManager %u