How to remove warnings like `Unknown media type ...`

Backup the file that is causing the errors and update the systems mime database:

sudo mv -vi /usr/share/mime/packages/kde.xml /usr/share/mime/packages/kde.xml.bak
sudo update-mime-database /usr/share/mime

This should fix the warnings.

This was discussed in Why does update-mime-database complain about uri/rtspt and other unusual types? It is caused by kde.xml and they have not fixed it yet. Here is a bug report.

Also it's uri/rtspu, not url/rtspu you should be grepping.

You should check /usr/share/mime/packages for the specific xml that contains the phrase you get .

For example, my problem was Unknown media type in type 'chemical/...... I found the file /usr/share/mime/packages/chemical-mime-data.xml.

Using cat on the file showed me that the package was the same chemical-mime-data V 0.94

So I ran:

sudo apt-get remove chemical-mime-data