vagrant_fix_for_kernel_4.4.0_caused_by_secure_boot.txt

# Source: http://askubuntu.com/questions/760671/could-not-load-vboxdrv-after-upgrade-to-ubuntu-16-04

# Follow instructions from 1 to 4 from the source url (stackoverflow).
# Then based from the comment also sign the following modules:`vboxnetflt`, `vboxnetadp`, and `vboxpci`. 
# After instruction 4: `sudo modprobe vboxdrv`, enter the following commands to finish signing the modules.

# Copy-paste the ff into the terminal:
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 modprobe vboxdrv
sudo modprobe vboxnetflt
sudo modprobe vboxnetadp
sudo modprobe vboxpci

# After doing so, you may run vagrant up successfully :)

https://askubuntu.com/questions/900118/vboxdrv-sh-failed-modprobe-vboxdrv-failed-please-use-dmesg-to-find-out-why
https://stegard.net/2016/10/virtualbox-secure-boot-ubuntu-fail/
https://askubuntu.com/a/802682