SQL-DATABASE ERROR

Database error in WoltLab Burning Board (): Link-ID == false, connect failed
mysql error: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (111)
mysql error number: 2002
mysql version: unknown
php version: 5.2.17
Date: 16.08.2018 @ 06:46
Script: /board.php?boardid=6&sid=ef51fd98ec63949795bafd0c8a18a177
Referer: