MySQL error in Plesk for Linux: Column count of mysql.user is wrong. Please use mysql_upgrade to fix this error

Symptoms

• When creating a database, modifying a database user settings or installing WordPress in Plesk, the operation fails with one of the the following error messages:

  PLESK_ERROR: Connection to the database server failed: Column count of mysql.user is wrong. Expected 42, found 39. Created with MySQL 50173, now running 50556. Please use mysql_upgrade to fix this error.

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  PLESK_ERROR: Column count of mysql.user is wrong. Expected 45, found 48. The table is probably corrupted

• A Plesk backup task finishes with the warning:

  PLESK_INFO: Warning: mysql “db_example”
  Not all the data was backed up into /path/to/db_example successfully. Total space: 200.00 GB; Available space: 150.00 GB; Mounted on: /. mysqldump: Couldn’t execute ‘SHOW FUNCTION STATUS WHERE Db = ‘db_example”: Column count of mysql.proc is wrong. Expected 21, found 20. Created with MariaDB 100134, now running 100313. Please use mysql_upgrade to fix this error (1558)

• Routines (stored procedures and functions) are not displayed in phpMyAdmin.

Cause

Some tables in the mysql database have incorrect schema.

Resolution

1. Connect to the server via SSH.

2. Upgrade the mysql database:

   # MYSQL_PWD=`cat /etc/psa/.psa.shadow` mysql_upgrade -uadmin -T –debug-check mysql