私のDebian JessieをDebian Unstableに変換/アップグレードすることはできません：
だから私はvimを使って/etc/apt/sources.listを編集しました。
deb http://ftp.u-picardie.fr/mirror/debian/ jessie main contrib non-free
deb-src http://ftp.u-picardie.fr/mirror/debian/ jessie main contrib non-free
deb http://security.debian.org/ jessie/updates main contrib non-free
deb-src http://security.debian.org/ jessie/updates main contrib non-free
# jessie-updates, previously known as 'volatile'
deb http://ftp.u-picardie.fr/mirror/debian/ jessie-updates main contrib non-free
deb-src http://ftp.u-picardie.fr/mirror/debian/ jessie-updates main contrib non-free
deb http://ftp.u-picardie.fr/debian/ testing main contrib non-free
deb-src http://ftp.u-picardie.fr/mirror/debian testing main contrib non-free
ただし、次のエラーが発生します。
W: Can't Recovery http://ftp.u-picardie.fr/debian/dists/testing/main/binary-amd64/Packages 404 Not Found [IP : 2001:660:4208:100::24 80]
W: Can't Recovery http://ftp.u-picardie.fr/debian/dists/testing/contrib/binary-amd64/Packages 404 Not Found [IP : 2001:660:4208:100::24 80]
W: Can't recovery http://ftp.u-picardie.fr/debian/dists/testing/non-free/binary-amd64/Packages 404 Not Found [IP : 2001:660:4208:100::24 80]
ベストアンサー1
URLの「/mirror」部分を忘れました。