Debian and Cinnamon and VirtualBox and Guest Additions

Cinnamon (Still not fixed):
I installed Debian into a VM, choosing Cinnamon as the desktop environment.
If the VBox setting "Enable 3D Acceleration" was not enabled, Cinnamon would indicate that it was running in software rendering mode, resulting in slow UI.
If the VBox setting "Enable 3D Acceleration" was enabled, Cinnamon would crash every time and run in Fallback mode which doesn't seem to permit any kind of interaction.
THE FIX was that simultaneously , I had VMWare running with a VM running Ubuntu. After shutting down the Ubuntu VM and starting the Debian VM with #D enabled, Cinnamon worked normally. Likely, there was a resource sharing issue between the two VMs.
Hmm. Part of it may be that I was interacting with the VM through Remote Desktop Connection. It looks like RDC might cause the fallback mode.
	Use VNC to connect to host
	start VM
		No prob
Weird. Now when I start the VM while using RDC, the error is gone. ??? I don't know.
Another possibility is the version of VirtualBox used. It seems to have no problems on my older install (4.3.30) but newer versions have trouble (5.0) https://www.virtualbox.org/ticket/14102

Guest Additions:
Wow, this was a pain. So first of all, log in as root, then execute this command:
	sudo apt-get install dkms
This instruction requires that the Debian install disk be in the drive. SO DUMB WHY DOESN'T IT PULL FROM A REPO??
I got that instruction from http://www.htpcbeginner.com/install-virtualbox-guest-additions-on-ubuntu-debian/
Next, from the VBox menu, select Devices/Insert Guest Additions CD
Then open the file browser, navigate to the CD contents, right click the window and select "Open in terminal"
Now run the following command because Debian is apparently berzerk:
	sudo sh VBoxLinuxAdditions.run
The 'sh' in the above command is what threw me for a loop. Trying to run the command without it gave me a permissions error.