VirtualBox Guest additions are a collection of device drivers and software application packages shipped along with VirtualBox. They are stored in an ISO image format inside the VirtualBox installation directory.
You will need to install Guest Additions inside a virtual machine once a guest operating has been installed.
Guest Additions improve the guest operating system’s performance and add extra features such as Mouse pointer integration, Shared folders, Better video support, Seamless windows, Time synchronization, Shared clipboard, and Automated logins.
You can read more in detail about guest additions on the Oracle VirtualBox user manual page.
Here, we will see how to install VirtualBox Guest additions on Debian 11 / Debian 10.
Prerequisites
First, update all the packages to the latest version.
sudo apt update sudo apt upgrade -y
Reboot your system in case the upgrade includes a Kernel update.
sudo reboot
Then, install the build tools and kernel headers for the current kernel.
sudo apt install -y build-essential linux-headers-$(uname -r)
Install VirtualBox Guest Additions on Debian
On the VM window, go to Devices » Insert Guest Additions CD Image.
Open a terminal and mount the CDROM to /mnt directory.
sudo mount /dev/cdrom /mnt
Execute the VirtualBox guest addition installer with sudo privileges.
cd /mnt sudo ./VBoxLinuxAdditions.run
Once the VirtualBox Guest additions installation is complete, reboot your system to complete the installation.
sudo reboot
If you do not get a full-screen view even after the reboot, minimize and maximize the window one time to get the full-screen view.
Sumber: disini