Install guest additions virtualbox | Setting share folder- Debian

VirtualBox is a very useful tool to install operating systems inside the main system. However, configuring the Virtualbox to share files and anable Auto-resize Guest Display between your main system and the system you installed in a VirtualBox

1. Setting share folder.
Go to setting your VM. Add a folder which you want to share, click OK and Start your machine.

Open a terminal and install the build-essential, dkms, and linux-headers packages. 
sudo apt install build-essential dkms linux-headers-$(uname -r)
Next, click to Devices and choose Insert Guest Additions CD image... or open machine setting > Storage and add iso file: C:\Program Files\Oracle\VirtualBox\VBoxGuestAdditions. (Power off your machine)
Now you can see on desktop appear the VBox_GAs iso file. Open it and run file autorun.sh "bash autorun.sh".

ERROR 1: VirtualBox Guest Additions: modprobe vboxsf failed
sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade -y
sudo apt-get install virtualbox-guest-dkms
reboot

ERROR 2: The folder contents could not be displayed or Permission denied
To gain access to this folder as a regular user, open the terminal in your guest system and add your user to the vboxsf group.
sudo adduser <your_username> vboxsf
e.g: sudo adduser laladee vboxsf
reboot