After installing some new packages in Arch-Linux I encountered this error message:

Unknown media type in type 'all/all'
Unknown media type in type 'all/allfiles'
Unknown media type in type 'uri/mms'
Unknown media type in type 'uri/mmst'
Unknown media type in type 'uri/mmsu'
Unknown media type in type 'uri/pnm'
Unknown media type in type 'uri/rtspt'
Unknown media type in type 'uri/rtspu'

According to Ana Guerrero, she said:

Those fake mimetypes are installed by kdelibs with the file /usr/share/mime/packages/kde.xml since long time ago. They are kept in kde4libs. In a recent version, update-mime-database became verbose about this unknown types, and that is why you get this error when you update stuff and then update-mime-database is run. It is unlikely to be changed.

A quick hack can fix this;

$ sudo rm /usr/share/mime/packages/kde.xml
$ sudo update-mime-database /usr/share/mime