Comment 5 for bug 2051987

Anna, can you have a look and see if the 'debian-sys-maint' user exists in the database (mysql table). Also you could check if the debian-sys-maint user can login with the password in /etc/mysql/debian.cnf

The mysql-server-9.0 package's postinst should create the user in the DB and the file in /etc/mysql/debian.cnf. If the user is missing, then perhaps it never got created (packaging bug), or the user has been removed at some point in the installation (charm bug? -- but I can't find any evidence), or some locking down/security process that's been done to the mysql instances?