Аз на Medibuntu хранилищата ги инсталирам по този начин.
Medibuntu free/Medibuntu non freesudo wget --output-document=/etc/apt/sources.list.d/medibuntu.list \
http://www.medibuntu.org/sources.list.d/$(lsb_release -cs).list
sudo apt-get --quiet update
sudo apt-get --yes --quiet --allow-unauthenticated install medibuntu-keyring
sudo apt-get --quiet update