

If you don't do that, you'll have to fiddle with /etc/fstab, which I won't go into here. (This is because I specified "auto-mount" as you see in the original post. Now, mount | grep vboxsf will show that there now is a mounted filesystem. it will compile and install the modules, but they won't be loaded yet. sudo mount /dev/cdrom /mnt/cdrom to mount the CD there.(You can of course use any directory as a mount-point. If necessary, sudo mkdir /mnt/cdrom to make a mount-point.


On the Devices menu of the running virtual machine, click " Insert Guest Additions CD Image.".And the VB documentation really didn't point that out. Well, I answered my own question with a little searching here in StackExchange: the virtualbox guest additions kernel modules were not installed.
