If you experience issues with installing the Virtualbox Guest Additions it could be that the build environment, dkms or kernel headers are not installed.

Messages typically look something like the following:

<pre class="brush: bash; title: ; notranslate" title="">
/tmp/vbox.0/Makefile.include.header:97: *** Error: unable to find the sources of your current Linux kernel. Specify KERN_DIR= and run Make again.  Stop

Install the following packages and retry the Guest Additions install:

<pre class="brush: bash; title: ; notranslate" title="">
# apt-get install build-essential dkms linux-headers-generic