Warning: mysqli_connect(): (HY000/2002): Can't connect to local server through socket '/var/lib/mysql/mysql.sock' (2) in /home/welcomet/public_gmap.ro/index.php on line 506

Warning: mysqli_error() expects exactly 1 parameter, 0 given in /home/welcomet/public_gmap.ro/index.php on line 506
I cannot connect to the database because: