Linux – How to access Guest (Linux) Filesystem from Host (Windows) in VirtualBox

There is no way to do this with the Guest extensions, however, setup normal Ubuntu file sharing on your guest and you can access the files using the virtual network between the host and the guest. The OSE version of VirtualBox doesn't have shared folders, and this is the recommended sharing method for VirtualBox as described here. How-To Geek has a tutorial here on how to do it with Ubuntu specifically, and it applies to everything outside of home folders as well.

The network driver is smart enough not to send the traffic over the wire, but will still be used to communicate with the guest. I have a few virtual machines I run and use like this, both on Mac and Windows.

OK, I think I figured it out.

There were a few gaps in my understanding:

Samba setup

• I realized that Samba users require their own authentication are not necessarily the same as UNIX usernames/passwords. So I created account with smbpasswd.
• I then confirmed that Samba setup was correct by mounting locally within the VM using smbmount, e.g., smbmount //localhost/share /mnt/test -o user=testuser,pass=password

Virtualbox setup

• I ended up wtih two NIC's on my VM - eth0 is default NAT adapter, then new eth1 is host-only
• In the VM, I gave eth1 a static IP address on the same subnet as the host-only network in VirtualBox File>Preferences>Network menu. The key I was missing is that the VM needs a DIFFERENT IP address than the host-only adapter on the host side. So the host-only adapter in VirtualBox is on 192.168.100.1, the static IP for Ubuntu guest is 192.168.100.2 (for example).
• Finally, once this was set up, I could see the Samba share under \\192.168.100.2\share\