SQL-DATABASE ERROR

Database error in WoltLab Burning Board: Link-ID == false, connect failed
mysql error: Can't connect to MySQL server on 'mysql.service' (113)
mysql error number: 2003
Date: 17.12.2018 @ 14:36
Script: /wbblite/misc.php?action=faq&sid=4b0c60b3962ebd707fa60faafa284c03
Referer: