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