Unable to start MySQL on Linux: unknown variable

Symptoms

• Plesk login page is unavailable:

  ERROR: PleskDBException: Unable to connect to database: mysql_connect(): No such file or directory /var/lib/mysql/mysql.sock (Error code: 2002). Please check that database server is started and accessible. (Abstract.php:69)

• MySQL fails to start. While attempt to start MySQL similar to the below error appears in the /var/log/mysqld.log or in /var/log/mariadb/mariadb.log with reference to different variable:

  [ERROR] /usr/libexec/mysqld: unknown variable 'set-variable=local-infile=0'[ERROR] Aborting

Cause

1. File /etc/my.cnf contains unsupported variable.

2. Misspelling in variable name.

Resolution

1. Connect to the server via SSH;

2. Check that variable name is set correctly in /etc/my.cnf;

3. If the issue persists, comment the line with variable name in /etc/my.cnf file under [mysqld] section.

4. Start MySQL service or restart if it is already running:

   # service mysqld restart

   or

   # service mariadb restart