- Dropping a file into the mu-plugins directory means that code runs automatically, without having to log into the admin. This comes in handy when you need to do things like force a WordPress admin user.
- If you want to load a normal plugin as a must use plugin, just drop the plugin folder into the mu-plugins directory and then create a plugin-loader.php file (any name will do) that does a require for the main plugin file.
- Files in the mu-plugins directory load alphabetically. If you need to manually control the load order, you can simply rename the files.
- You can move or rename the mu-plugins directory by setting these constants in your wp-config.php file:
define( 'WPMU_PLUGIN_DIR', __DIR__ . '/wp-content/required-plugins' ); define( 'WPMU_PLUGIN_URL', 'http://mydomain.com/wp-content/required-plugins' );
Reference: https://wpscholar.com/blog/wordpress-must-use-plugins/