Thanks for the quick answer! Firstly, as you can see in the attached dpkg terminal log, I believe mysql_upgrade tried to run as (mysql) root:
.... Installing new version of config file /etc/mysql/mysql.conf.d/mysqld.cnf ... update-alternatives: using /etc/mysql/mysql.cnf to provide /etc/mysql/my.cnf (my.cnf) in auto mode mysql_upgrade: Got error: 1045: Access denied for user 'root'@'localhost' (using password: NO) while connecting to the MySQL server Upgrade process encountered error and will not continue. .... Secondly, regarding the debian-sys-maint DB user, phpMyAdmin tells me it has no password and has "ALL PRIVILEGES". I noticed this user only today :)). ** Changed in: mysql-5.7 (Ubuntu) Status: Incomplete => New -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1567612 Title: package mysql-server-5.7 not installed failed to install/upgrade: subprocess installed post-installation script returned error exit status 11 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/mysql-5.7/+bug/1567612/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs