Exception class: RuntimeException()

ERROR: Cannot connect to MySQL database.
Possible reasons:

• MySQL is not configured propertly in config.lua.
• MySQL server is not running.

SQLSTATE[HY000] [2002] No route to host

File: /var/www/html/system/database.php
Line: 125


Backtrace:

#0 /var/www/html/system/init.php(141): require_once()
#1 /var/www/html/index.php(188): require_once('...')
#2 {main}