Debian and Virtualbox (updated for Stretch/9.3)

Dealing with guest additions on a fresh VM, and VirtualBox in general.

Installing guest additions:

# apt update; apt upgrade (reboot after this if kernel upgrade)
# apt install build-essential linux-headers-$(uname -r)
(Insert Guest Additions CD image...) get optical drive device name with 'blkid' if needed.
# mount /dev/sr0 /media/cdrom
# /media/cdrom/VBoxLinuxAdditions.run
	^ May show weird screen at completion, 
	  I repeat it twice for a more intuitive result.
	^ If you get permission denied, you may have success with using an interpreter:
	  # sh ./VBoxLinuxAdditions.run 
# shutdown -r now

Adding Virtualbox itself to a Debian 8 installation (old info, check this now):

# nano /etc/apt/sources.list
^ deb http://download.virtualbox.org/virtualbox/debian jessie contrib

# wget -q https://www.virtualbox.org/download/oracle_vbox_2016.asc -O- | sudo apt-key add -
# wget -q https://www.virtualbox.org/download/oracle_vbox.asc -O- | sudo apt-key add -
# apt-get update; apt-get install Virtualbox-5.1 dkms

Adjusting console resolution:

# nano /etc/default/grub
	^ add 'nomodeset' to GRUB_CMDLINE_LINUX_DEFAULT
	  add 'GRUB_GFXPAYLOAD_LINUX=1280x1024x16' (as an example) on the bottom of file.
	  NOTE: check for compatible resolutions with 'vbeinfo' in grub at boot, push 'c'.
# update-grub; shutdown -r now

Turn off login spam (goes for any installation really...):

# nano /etc/update-motd.d/10-uname
	^ comment it awayyyyy.
# nano /etc/motd
	^ LCTRL+K(kkkkkkkkkkk4thedarkness and put something custom in issue(+.net) instead).

Since Virtualbox is a type 2 hypervisor, hardware support is not needed (VT-x, AMD-V) but supports it.

Helpful Resources:
VBoxManage Reference