After installing virtualbox-guest-x11 in my guest system, I'm having a black screen. I'm using Kubuntu 17.10, on a Windows 10 host. Processor Intel(R) Core(TM) i5-3230M CPU @ 2.60GHz, 8 GB RAM. Steps: 1) Install Kubuntu 17.10 in Virtualbox. 2) Install insert guest aditions iso (execute /media/cdrom /media/cdrom/VBoxLinuxAdditions.run/). 3) Restart 4) sudo apt install virtualbox-guest-x11 5) Restart and I have a black screen.
Please ask for help in a forum of your distribution. It might be related to video drivers.