if your debian-lxde is stuck to a fixed resolution…

virtualbox auto resize guest display


make shure that:

virtualbox auto resize guest display1

LXDE auto resize screen VirtualBox

Package Installation After setting up your new Lubuntu VM you’ll need to update the sources.list and install several components. Lubuntu doesn’t come with various compiling tools, such as gcc and make, and so those must be manually installed:

sudo apt-get update
sudo apt-get install build-essential dkms gcc make

Next you’ll need to make sure the kernel headers are installed:

sudo apt-get install linux-headers-$(uname -r)

Now you’re ready to install the guest additions.

1. mount Guest Additions CD via Menu
2. cp -R all to a temp folder /virtualbox
3. cd /virtualbox and run VBoxLinuxAdditions.run

reboot and you should be good.