deb http://ftp.de.debian.org./debian stretch main contrib non-free deb http://ftp.de.debian.org./debian stretch-updates main contrib non-free deb http://ftp.de.debian.org./debian stretch-proposed-updates main contrib non-free deb http://security.debian.org./ stretch/updates main contrib non-free # deb http://ftp.de.debian.org./debian stretch-backports main contrib non-free