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Use the Oracle VM VirtualBox Manager GUI, Select File --> Preferences, then in the VirtualBox - Settings window, select Network. In the Network pane, select the Host-only Networks tab and check you have an entry named vboxnet0. If not, click the add host-only network button to add it. Make sure, that you defined following ip address subnet to it: 192.168.56.1
If you already have one Host-only Network configuration in the Virtual Box settings which you cannot change, please create a new one eg. vboxnet1 with subnetwork 192.168.56.1. You will afterwards have to change the machine_setup script appropriatelly.