Database connection failed!

Stack Trace:

File: /var/www/html/ojs/ojs-3.2.1-4/lib/pkp/includes/bootstrap.inc.php line 41
Function: PKPApplication->__construct()

File: /var/www/html/ojs/ojs-3.2.1-4/index.php line 65
Function: require("/var/www/html/ojs/ojs-3.2.1-4/lib/pkp/includes/bootstrap.inc.php")