Database connection failed!

Stack Trace:

File: /var/www/OJS3.0/classes/core/Application.inc.php line 36
Function: PKPApplication->__construct()

File: /var/www/OJS3.0/lib/pkp/includes/bootstrap.inc.php line 55
Function: Application->__construct()

File: /var/www/OJS3.0/index.php line 72
Function: require("/var/www/OJS3.0/lib/pkp/includes/bootstrap.inc.php")