Exception class: RuntimeException()

ERROR: Cannot connect to MySQL database.
Possible reasons:

• MySQL is not configured propertly in config.lua.
• MySQL server is not running.

SQLSTATE[HY000] [2002] Connection refused


Backtrace:

#0 /var/www/html/system/init.php(128): require_once()
#1 /var/www/html/index.php(178): require_once('/var/www/html/s...')
#2 {main}