Database connection failed!

Stack Trace:

File: /var/www/html/classes/core/Application.inc.php line 38
Function: PKPApplication->PKPApplication()

File: /var/www/html/lib/pkp/includes/bootstrap.inc.php line 59
Function: Application->Application()

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