$ sudo sh VBoxLinuxAdditions.run
Verifying archive integrity... All good.
Uncompressing VirtualBox 4.3.24 Guest Additions for Linux............
VirtualBox Guest Additions installer
You appear to have a version of the VBoxGuestAdditions software
on your system which was installed from a different source or using a
different type of installer.  If you installed it from a package from your
Linux distribution or if it is a default part of the system then we strongly
recommend that you cancel this installation and remove it properly before
installing this version.  If this is simply an older or a damaged
installation you may safely proceed.

Do you wish to continue anyway? [yes or no]
no

Cancelling installation.