After investigating this thoroughly, it turned out debian-sys-maint’s password differed between /etc/mysql/debian.cnt and the database. After a proper SET PASSWORD FOR 'debian-sys-maint'@'localhost' everything seems ok (and the upgrade ran smoothly), so feel free to close this bug.
After investigating this thoroughly, it turned out debian-sys-maint’s password differed between /etc/mysql/ debian. cnt and the database. After a proper SET PASSWORD FOR 'debian- sys-maint' @'localhost' everything seems ok (and the upgrade ran smoothly), so feel free to close this bug.