How can I get virtualbox to run with a hosts-only adapter?

It seems like these adapters are added in Virtual Box -> preferences -> network.

Since Virtualbox 5.2.xxx, the location to create a host-only network has now changed to File -> Host Network Manager...

Clicking on the Create button in the Host Network Manager window will create a host-only network called vboxnet0, which you can then use within the VM settings.

In order to have bidirectional access please follow next steps ...

It's very important that after (Virtual Box -> Preferences -> Network -> vboxnet0) to configure your firewall.

1. Allow routing (ip.forwarding)
2. Allow NAT through fireall

OSX firewall sample

    # (I) Firewall config /etc/sysctl.conf
    sysctl -w net.inet.ip.forwarding=1 net.inet.ip.fw.enable=1
    sysctl -a net.inet.ip.forwarding net.inet.ip.fw.enable

    ipfw list
    ... shoud have ....
    net.inet.ip.forwarding=1
    net.inet.ip.fw.enable=1


    # (II) Enable nat access to /etc/pf.conf
    #============add your host-only vlan =================
    # this commented lines doesn't work after computer reboot
    #nat on en0 from vboxnet0:network -> (en0)
    #nat on en3 from vboxnet0:network -> (en3)
    # this will work in any situation
    nat on en0 from 10.1.100.0/24 to any -> (en0)
    nat on en3 from 10.1.100.0/24 to any -> (en3)        
    #==========================        

    # Reload pf
    pfctl -f /etc/pf.conf
    pfctl -e

Enjoy

You can do it command line (since the UI location is not consistent) like so: VBoxManage hostonlyif create. This will create a vboxnet0 interface ready for use.