Warning: mysqli_connect(): (HY000/2002): Connection refused in /var/www/html/core/mysql.php on line 2

Fatal error: Uncaught Error: Call to a member function set_charset() on boolean in /var/www/html/core/mysql.php:4 Stack trace: #0 /var/www/html/include.php(6): require() #1 /var/www/html/index.php(3): require_once('/var/www/html/i...') #2 {main} thrown in /var/www/html/core/mysql.php on line 4