Install virtualbox guest additions on elementary OS

Para instalar hay que hacer los siguientes pasos:

Instalar los headers del kernel

$ sudo apt-get install build-essential module-assistant

ubicar la entrada en el dev del cdrom y montar el iso de virtualbox additions

$ lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0    20G  0 disk 
├─sda1   8:1    0    18G  0 part /
├─sda2   8:2    0     1K  0 part 
└─sda5   8:5    0     2G  0 part [SWAP]
sr0     11:0    1  61.7M  0 rom  

$ cd ~/
$ mkdir vbox

# mount the cd rom
$ sudo mount /dev/sr0 ~/vbox
mount: block device /dev/sr0 is write-protected, mounting read-only

Instalar las virtualbox additions

$ cd vbox/
~/vbox$ sudo ./VBoxLinuxAdditions.run
Verifying archive integrity... All good.
Uncompressing VirtualBox 4.3.10 Guest Additions for Linux............
VirtualBox Guest Additions installer
Copying additional installer modules ...
Installing additional modules ...
Removing existing VirtualBox DKMS kernel modules ...done.
Removing existing VirtualBox non-DKMS kernel modules ...done.
Building the VirtualBox Guest Additions kernel modules ...done.
Doing non-kernel setup of the Guest Additions ...done.
Starting the VirtualBox Guest Additions ...done.
Installing the Window System drivers
Installing X.Org Server 1.11 modules ...done.
Setting up the Window System to use the Guest Additions ...done.
You may need to restart the hal service and the Window System 

Eso es todo.

Información tomada de

http://www.binarytides.com/install-virtualbox-guest-additions-elementary-os-luna/