A toute fin utile, la réponse à ma question est dans la FAQ du how-to consacré :
Can I `apt-get arch-upgrade` from an already installed i386 debian?
No. You need to reinstall on a newly formatted partition or disk, by either running cdebootstrap / debootstrap from your running installation or using the Debian-Installer.
# The Debian GNU/Linux AMD64 HOW-TO
Posté par pini . En réponse au message Upgrade d'un PC IA32 vers AMD64. Évalué à 1.
Can I `apt-get arch-upgrade` from an already installed i386 debian?
No. You need to reinstall on a newly formatted partition or disk, by either running cdebootstrap / debootstrap from your running installation or using the Debian-Installer.
Le how-to est là :
https://alioth.debian.org/docman/view.php/30192/21/debian-am(...)
Désolé pour le bruit.