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

You get more information about the problem in our knowledge base: http://www.woltlab.com/help/?code=2005

Information:

error message: Connecting to MySQL server 'mysql' failed.
error code: 2005
sql type: MySQLDatabase
sql error: Unknown MySQL server host 'mysql' (1)
sql error number: 2005
sql version:
file: /var/www/usersites/a/ac/acmboard/htdocs/wcf/lib/system/database/MySQLDatabase.class.php (29)
php version: 5.2.6-1+lenny4
wcf version: 1.0.7
date: Fri, 27 Jan 2012 19:34:15 +0000
request: /
referer:

Stacktrace:

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