Fatal error: Connecting to MySQL server 'localhost' failed.

You get more information about the problem in our knowledge base: http://www.woltlab.com/help/?code=2002

Information:

error message: Connecting to MySQL server 'localhost' failed.
error code: 2002
sql type: MySQLDatabase
sql error: No such file or directory
sql error number: 2002
sql version:
file: /var/www/vhosts/dobifreunde.de/httpdocs/wcf/lib/system/database/MySQLDatabase.class.php (29)
php version: 5.4.45
wcf version: 1.0.11 pl 4 (Horizon)
date: Mon, 18 Mar 2019 23:30:48 +0000
request: /index.php?form=UserLogin&s=e31b26e829daa0ccb5a8ca536f73cea7dd96b227
referer:

Stacktrace:

#0 /var/www/vhosts/dobifreunde.de/httpdocs/wcf/lib/system/database/Database.class.php(76): MySQLDatabase->connect()
#1 /var/www/vhosts/dobifreunde.de/httpdocs/wcf/lib/system/WCF.class.php(270): Database->__construct(...)
#2 /var/www/vhosts/dobifreunde.de/httpdocs/wcf/lib/system/WCF.class.php(88): WCF->initDB()
#3 /var/www/vhosts/dobifreunde.de/httpdocs/global.php(18): WCF->__construct()
#4 /var/www/vhosts/dobifreunde.de/httpdocs/index.php(7): require_once('/var/www/vhosts...')
#5 {main}