Der Standardpfad zum MySQL Socket passt wohl auf deinem System nicht, deshalb solltest du die murmur.ini anpassen (genauer die Variable dbOpts).
# If you wish to use something other than SQLite, you'll need to set the name # of the database above, and also uncomment the below. # Sticking with SQLite is strongly recommended, as it's the most well tested # and by far the fastest solution. # dbDriver=QMYSQL dbUsername=lala ... dbOpts="UNIX_SOCKET=/var/path/to/mysql.sock" ...
Weitere mögliche Optionen für dbOpts gibt es hier: Servereinstellungen - dbopts.