Virtual box Full screen mode for debian

1. Login as root;
2. Update your APT database with apt-get update;
3. Install the latest security updates with apt-get upgrade;
4. Install required packages with apt-get install build-essential module-assistant;
5. Configure your system for building kernel modules by running m-a prepare;
6. Click on Install Guest Additions… from the Devices menu, then run mount /media/cdrom.
7. Run sh /media/cdrom/VBoxLinuxAdditions.run, and follow the instructions on screen

Virtual box VM communication

In order to communicate between the VM's and also to connect to  an internet, please follow the below steps

1) Select Settings->network-> Attached to :Internal network from virtual Box GUI

2) Once VM boots up, we need to configure static IP's for an interface  to communicate between the VM's.

You need to stop networking service in VM's from resetting an interface.

3) Suppose if you want to connect to an internet  you need to configure NAT network 

File->preferences->Network  and add NAT networks