Install VirtualBox Additions on CentOS 8

Login as root and install packages required for building kernel modules and elfutils-libelf-devel as a prerequisite for the additions.

# dnf install gcc kernel-devel kernel-headers dkms make bzip2 perl elfutils-libelf-devel

From the VirtualBox window, insert the guest-tools CD image.
Devices -> “Insert Guest Additions CD Image”

Mount the virtual CD-ROM drive and install the VirtualBox Additions.

# mkdir /mnt/cdrom
# mount /dev/cdrom /mnt/cdrom
# cd /mnt/cdrom/
# sh ./ --nox11
# reboot