Symptoms

• After upgrading MariaDB, the MariaDB service fails to start with the following error message in /var/log/mariadb/mariadb.log or /var/log/mysql/error.log:

  [Note] InnoDB: Starting shutdown...
  [ERROR] Plugin 'InnoDB' init function returned error.
  [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
  [Note] Plugin 'FEEDBACK' is disabled.
  [ERROR] Unknown/unsupported storage engine: InnoDB
  [ERROR] Aborting

  or MariaDB service returns the following error:

  # service mariadb status
  ERROR! MariaDB is running but PID file could not be found

• The same error may appear during Plesk upgrade or update.

Cause

MariaDB database server was not properly upgraded.

Resolution

1. Connect to the Plesk server via SSH.

2. Shut down MariaDB service:

   # mysqladmin -uadmin -p`cat /etc/psa/.psa.shadow` -h127.0.0.1 --protocol=tcp shutdown

3. Remove the incorrect service script and reload systemctl configuration:

   # rm -f /etc/init.d/mysql && systemctl daemon-reload

4. Start the MariaDB service:

   # service mariadb restart

5. Enable MariaDB service start on boot:

   # systemctl enable mariadb