VirtualBox 5 is unable to create a host-only adapter on Ubuntu 16.04

Solution 1:

It turns out that the solution to the networking problem is a separate module that must be signed to allow this specific function. As stated in the signing solution here: https://askubuntu.com/a/768310/254069

VBoxManage hostonlyif create needs the following modules to also be accessible (modprobe):

openssl req -new -x509 -newkey rsa:2048 -keyout MOK.priv -outform DER -out MOK.der -nodes -days 36500 -subj "/CN=MOK Signing/"

sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 ./MOK.priv ./MOK.der $(modinfo -n vboxdrv)
sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 ./MOK.priv ./MOK.der $(modinfo -n vboxnetflt)
sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 ./MOK.priv ./MOK.der $(modinfo -n vboxnetadp)
sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 ./MOK.priv ./MOK.der $(modinfo -n vboxpci)

sudo mokutil --import MOK.der

Restart and "Enroll MOK"

$ VBoxManage hostonlyif create
0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%
Interface 'vboxnet1' was successfully created