Fix kernel driver not installed in VirtualBox

Every time I install a new kernel version in my Debian Testing, I mess up the Virtual Box configuration. The message that comes from VirtualBox is pretty clear:

Kernel driver not installed (rc=-1908)

The VirtualBox Linux kernel driver (vboxdrv) is either not loaded or there is a permission problem with /dev/vboxdrv. Please reinstall the kernel module by executing

'/etc/init.d/vboxdrv setup'

as root. [...]

Here the kernel version has changed under the hood, and VirtualBox should be notified about that. The solution lies in the message above: run /etc/init.d/vboxdrv setup as root and everything should be fine.

Missing kernel headers

If you are a bit less lucky like me, you might not have the latest kernel headers at hand, and because of that vboxdrv cannot work properly. That's not a problem at least on Debian-based distros. You just have to install them with:

sudo apt-get install linux-headers-<kernel-version>-<processor>

If you don't remember the kernel version or the architecture of your processor, the small utility uname comes to the rescue. It's a Unix app that prints some information about the operating system running on your machine. Invoke it with the flag -r to print the kernel release. In my case it is:

4.5.0-1-amd64

That's enough for apt-get to do its job. Let's glue those parts together:

sudo apt-get install linux-headers-$(uname -r)

And you're done.

Sources

Wikipedia - Uname (link)
AskUbuntu - How do I install kernel header files? (link)