So, I’ve been having this issue with upgrading MySQL 5.7 on a Ubuntu 16.04 server. It kept erroring out. Even uninstalling MySQL and reinstalling it did not help. Until I found this post by iqbal_cs:
root@iqbal: mysql -u root -p
Enter password:
mysql> GRANT ALL PRIVILEGES ON *.* TO 'debian-sys-maint'@'localhost' IDENTIFIED BY '<your password>';
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements
If the error(1819) is raised, type this on the mysql terminal
mysql> uninstall plugin validate_password;
Then restart mysql: systemctl restart mysql
Finally
apt install -f
to fix broken dependencies
If error continues, enter again to mysql terminal, login: type this:
mysql> GRANT ALL PRIVILEGES ON *.* TO 'debian-sys-maint'@'localhost' IDENTIFIED BY '<your password>'
apt -f install for the last time.