An automatically installed Debian MariaDB (drop-in replacement for MySQL) security update, has broken all v15.x appliances that rely on MariaDB database engine. That means that all LAMP based appliances, such as WordPress, Drupal, Joomla and about 70% of the library will not have a functioning MySQL-compatible DB engine running.

The good news is that it's really easy to fix. Simply reinstall the 'default-mysql-server' package like this:

apt update
apt install default-mysql-server

For more info, or if you have any questions, please check out the blog post

Regards,
Jeremy
TurnKey Linux