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: /is/htdocs/wp1157274_O4NUXCFUHX/www/forum/wcf/lib/system/database/MySQLDatabase.class.php (29)
php version: 5.6.38-he.0
wcf version: 1.0.11 pl 4 (Horizon)
date: Sun, 21 Oct 2018 14:52:18 +0000
request: /index.php?form=Mail&userID=3&s=76f15710e23cd0ad282de8d62daa260ca2d53ecd
referer:

Stacktrace:

#0 /is/htdocs/wp1157274_O4NUXCFUHX/www/forum/wcf/lib/system/database/Database.class.php(76): MySQLDatabase->connect()
#1 /is/htdocs/wp1157274_O4NUXCFUHX/www/forum/wcf/lib/system/WCF.class.php(270): Database->__construct(...)
#2 /is/htdocs/wp1157274_O4NUXCFUHX/www/forum/wcf/lib/system/WCF.class.php(88): WCF->initDB()
#3 /is/htdocs/wp1157274_O4NUXCFUHX/www/forum/global.php(18): WCF->__construct()
#4 /is/htdocs/wp1157274_O4NUXCFUHX/www/forum/index.php(7): require_once('/is/htdocs/wp11...')
#5 {main}