Symptoms

The following error appears in Plesk while starting mysql service:

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)

The following error is present in system log (/var/log/messages ):

CONFIG_TEXT: [ERROR] Missing system table mysql.roles_mapping; please run mysql_upgrade to create it

Website shows 'Error establishing a database connection' error and trying to access website databases at Plesk > Domains > example.com > Databases results in the error:

PLESK_ERROR: Unknown column 'Event_priv' in 'field list  

Cause

Failed MySQL upgrade.

Resolution

Connect to the server using SSH and complete the MySQL upgrade using the following command:

# MYSQL_PWD=`cat /etc/psa/.psa.shadow` mysql_upgrade -u admin --host localhost --port 3306