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 @ 10:04
Script: /profile.php?userid=199&sid=f33d4a9e3fff9d0a8bd5584403bf1381
Referer: