MySQL/MariaDB schema upgrade error: Incorrect database name '#mysql50#.ssh'

Symptoms

• Plesk upgrade fails during MySQL/MariaDB upgrade with one of these errors:

  Got error: 1102: Incorrect database name '#mysql50#example.database' when selecting the database

  Failed to install 'C:\ParallelsInstaller\parallels\PANEL-WIN_17.5.3\dist-msi-Mic
  rosoft-2003-i386\mysql-admin_mu067.msi': Fatal error during installation. (Error
  code 1603)

• Upgrading the MySQL/MariaDB schema with mysql_upgrade fails:

  Failed to ALTER DATABASE `#mysql50#.ssh` UPGRADE DATA DIRECTORY NAME
  Error: Incorrect database name '#mysql50#.ssh'
  Running 'mysqlcheck with default connection arguments
  mysqlcheck: Got error: 1102: Incorrect database name '#mysql50#.ssh' when selecting the database
  FATAL ERROR: Error during call to mysql_check for upgrading the tables names.

• There's a folder whose name starts with a dot "." in /var/lib/mysql/ directory.

Cause

The folder starting with a dot (".") in the MySQL/MariaDB datadir directory prevents the mysqlcheck command from running correctly.

Resolution

Move the dot folder outside datadir, which by default is:

• /var/lib/mysql on Linux
• %plesk_dir%Databases\MySQL\data\ or %plesk_dir%MySQL\Data\ on Windows

Note: If it's not any of the above, its location is defined by and can be found in the my.ini or my.cnf config files.