Symptoms

1. Unable to start mariadb or mysql service after upgrade with the following error message in MySQL error log in /var/log/mariadb/mariadb.log or /var/log/mysql/error.log:

CONFIG_TEXT: [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

The same error may appear during Plesk upgrade or update

2. Plesk is not accessible with:

PLESK_ERROR: ERROR: Plesk\Exception\Database: DB query failed: SQLSTATE[HY000]: General error: 1 Can't create/write to file '/var/tmp/#sql_5f1_0.MAI' (Errcode: 2), query was: DESCRIBE `sessions`
Additionally, an exception has occurred while trying to report this error: Zend_Exception
No entry is registered for key 'translate' (Mysql.php:53)

Cause

Mariadb or mysql service was not stopped properly after the upgrade.

Resolution

1. Connect to the server via SSH.

2. Stop the service properly by the following command::

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

3. Restart mariadb or mysqld service:

   # systemctl restart mariadb 
   # systemctl restart mysqld