virtualbox.org

I'm running an Ubuntu 12.04 VM under Virtualbox 4.2.6 and am trying to install the Guest Extensions primarily to keep the guest clock synched with the host.
Since the virtual machine is headless I don't want the guest extensions that require X.

apt-cache search virtualbox

shows:

virtualbox-guest-utils - x86 virtualization solution - non-X11 guest utilities

So I figured this was what I wanted, so I ran:

apt-get install virtualbox-guest-utils

But doing that shows:

The following NEW packages will be installed:
  dkms fakeroot libfontenc1 libgl1-mesa-dri libice6 libllvm3.0 libpixman-1-0 libsm6 libxaw7 libxcomposite1 libxdamage1
  libxfixes3 libxfont1 libxkbfile1 libxmu6 libxpm4 libxrandr2 libxrender1 libxt6 virtualbox-guest-dkms
  virtualbox-guest-utils virtualbox-guest-x11 x11-common x11-xkb-utils xfonts-base xfonts-encodings xfonts-utils
  xserver-common xserver-xorg-core

So if the virtualbox-guest-utils package is supposed to install the non X11 utilities, then why is it trying to install xserver-common and xserver-xorg-core???

Is the installation package for Ubuntu 12.04 buggy?

This will install the guest additions from the ubuntu repos, which is not what you wannt.
Use the ISO provided by the Virtualbox installation, located in /usr/share/virtualbox

It seems that installing the Guest Extensions from the ISO does so by compiling them. This means that make and gcc are installed on the machine - something that drags in a bunch of stuff that I'll only need once. As it happens I did install using the ISO and because I saw an error about X I wasn't sure if anything had actually been installed or just the X stuff was missing (as desired).

The error is simply about the X stuff missing and so the X extentions couldnt be installed, just as you wished.