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: 18.01.2019 @ 13:52
Script: /wbblite/search.php?sid=0c0d8e259ea5ecfd4bdf8c906e3eee69
Referer: