Virtual Box: Install Guest Additions

create directory and mount.

sudo mkdir -p /mnt/cdrom
sudo mount /dev/cdrom /mnt/cdrom 

run the Guest Additions CD image.

 cd /mnt/cdrom
 sudo ./VBoxLinuxAdditions.run
 
 sudo reboot

Reference: https://linuxconfig.org/install-virtualbox-guest-additions-on-linux-guest