Unable to log into Plesk: Unable to connect to database: mysql_connect(): Permission denied /var/lib/mysql/mysql.sock

Symptoms

• Unable to log in to Plesk, the following error appears:

  ERROR: PleskDBException: Unable to connect to database: mysql_connect(): Permission denied /var/lib/mysql/mysql.sock (Error code: 2002). 

  ---

  ERROR: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000] [2002] Permission denied' in /usr/local/psa/admin/externals/Zend/Db/Adapter/Pdo/Abstract.php

• Unable to start
mariadb service with the following error:

  systemd[1]: Starting MariaDB database server...
  mariadb-prepare-db-dir[4030]: chmod: changing permissions of Б─≤/var/lib/mysqlБ─≥: Operation not permitted
  mariadb-prepare-db-dir[4030]: Initializing MySQL database
  mariadb-prepare-db-dir[4030]: chown: changing ownership of Б─≤/var/lib/mysqlБ─≥: Operation not permitted
  mariadb-prepare-db-dir[4030]: Cannot change ownership of the database directories to the 'mysql'
  mariadb-prepare-db-dir[4030]: user. Check that you have the necessary permissions and try again.
  mariadb-prepare-db-dir[4030]: Initialization of MySQL database failed.

• Unable to access MySQL/MariaDB database. The following error appears if trying to log in to database using
mysql utility:

  ERROR 1018 (HY000): Can't read dir of './db-name/' (errno: 13)

• The permissions of
/var/lib/mysql/ are different from listed below:

  # ls -ld /var/lib/mysql
  drwxr-xr-x 5 mysql mysql 4096 Apr 20 13:05 /var/lib/mysql

Cause

Incorrect permissions for
/var/lib/mysql/ directory and its subdirectories.

Resolution

1. Log in to the server via SSH;

   Note: if direct SSH access to the server is not possible, contact server administrator for further assistance.

2. Set proper owner to the directory and files:

   # chown -R mysql:mysql /var/lib/mysql
   # find /var/lib/mysql/* -type d -exec chmod 0700 {} ;
   # find /var/lib/mysql/* -type f -exec chmod 0660 {} ;

   For Debian/Ubuntu

   # chmod 700 /var/lib/mysql

   For RHEL/CentOS

   # chmod 755 /var/lib/mysql