Updating VBoxGuestAdditions between minor versions is a pain. So here's a lovely shell script... yay!!!1! (Boo!)

update_vbga.sh

#!/bin/bash
#
# Upgrade VirtualBox Guest Additions
#
# This script removes VirtualBox Guest Additions v4.2.6 from the mirror
# machines when brought up using Vagrant, and installs v4.3.6 instead. This
# makes the version of VirtualBox being used in this repository the same as
# is used in the off-site backup and main Puppet repositories.

set -ex

$VBGA_DIR="/opt/VBoxGuestAdditions-4.2.6"
$MNT_DIR="/mnt/vbga"

# First, let's uninstall VBoxGuestAdditions-4.2.6
sudo .$DIR/uninstall.sh

# Now, let's check we've actually uninstalled it all by checking to see if
# $DIR is empty. If it is, tidy up after ourselves and remove $DIR. If not,
# hard fail by echoing out.
if [ "$(ls -A $DIR)" ]; then
  echo "Uh-oh! $DIR is not empty."
else
  echo "Yay! $DIR is empty. Removing VirtualBox Guest Additions v4.2.6..."
  sudo rm -rf $DIR/*
fi

# Download VBGA ISO, create mountpoint and mount
wget http://download.virtualbox.org/virtualbox/4.3.6/VBoxGuestAdditions_4.3.6.iso /home/vagrant/
sudo mkdir -p $MNT_DIR
sudo mount -o loop VBoxGuestAdditions_4.3.6.iso $MNT_DIR

# Run installer script
touch /var/log/vbga_install.log
sudo ./$MNT_DIR/VBoxLinuxAdditions.run > /var/log/vbga_install.log

# Remove install log
sudo rm -f /var/log/vbga_install.log