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: 16.10.2018 @ 10:02
Script: /search.php?sid=12a4e6ecfc45e7aaf3e232ea45329345
Referer: