SQL-DATABASE ERROR

Database error in WoltLab Burning Board (): Link-ID == false, connect failed
mysql error: Unknown MySQL server host 'mysql5.service' (1)
mysql error number: 2005
mysql version: unknown
php version: 4.4.8
Date: 24.09.2018 @ 13:39
Script: /jgs_portal_links.php?action=suche2_starten&buchstabe=A
Referer: