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: 24.05.2019 @ 05:47
Script: /thread.php?postid=25441&sid=cb9bb5f27bcbcfac0a6af18005445eb5
Referer: