I’m trying to install the Virtualbox Guest Additions on Whonix Gateway 9.4, on a Debian Jessie host. I get the following error. Can anyone suggest a remedy?
Unable to insert the virtual optical disk /home/user/.config/VirtualBox/VBoxGuestAdditions_4.3.18.iso into the machine Whonix-Gateway. Would you like to try to force insertion of this disk? Could not mount the media/drive '/home/user/.config/VirtualBox/VBoxGuestAdditions_4.3.18.iso' (VERR_PDM_MEDIA_LOCKED).
Thanks, but I did read that and it amounts to “don’t use Jessie for this!” I.e., try it on a Wheezy host, which I shall now do.
The instructions for Wheezy work perfectly, thank you.
I needed the guest additions for the mouse integration, because I’m accessing the host machine with VNC, and VNC can’t pass through the right-control keystroke required (in the basic Virtualbox vm) to switch the mouse out of the vm to the host.
I see that the guest additions include “x11” so I’ll see if it is possible to get a vnc session directly to the vm.
EDIT: I mean that I know “x11” might relate to the x-terminal resolution. However, Virtualbox is supposed to be capable of hosting VNC sessions to guests, which i wasn’t able to do before on a basic vm, but maybe I can now with the guest additions.
EDIT: Two minutes later I realize that vnc to WHONIX vm isn’t going to be possible because… Tor! 
If it was possible it would represent a serious flaw.
EDIT: Now I’m thinking: Perhaps it might work if the vm, running a vnc server, initiates the connection to a vnc viewer operating in “listen” mode.
For guest additions, it doesn’t matter what your host operating is. Depends on guest operating system, which is Debian wheezy as of Whonix 9.x.
VirtualBox also has some RDP feature, that requires the proprietary VirtualBox extension pack. Never used it. Dunno. Apart from this it could even be a secure concept. (Dunno about actual implementation.)
Another thing… Maybe this helps: