I tried again. This time journalctl -xe throws this useful error:
mysqld[23361]: mysqld: Can't read dir of '/etc/mysql/conf.d/' (Errcode: 2 - No such file or directory)
Repairing tables
mysql.proxies_priv OK
Upgrade process completed successfully.
Checking if update is needed.
Setting up mysql-server (5.7.12-0ubuntu1) ...
I tried again. This time journalctl -xe throws this useful error: conf.d/ ' (Errcode: 2 - No such file or directory)
mysqld[23361]: mysqld: Can't read dir of '/etc/mysql/
Easy fix now: mysql.conf. d/ /etc/mysql/conf.d/
sudo cp -r /etc/mysql/
Successfully migrated databases to 5.7
Repairing tables
mysql.proxies_priv OK
Upgrade process completed successfully.
Checking if update is needed.
Setting up mysql-server (5.7.12-0ubuntu1) ...