Error: Virtualbox unable to insert the virtual optocal disk C:\ Program Files \ Oracle \ Virtualbox \ VBoxguestadditions.iso into the machine Xubuntu

I am a beginner and just installed VM VirtualBox 6.1.16140961-Win and xubuntu-18.04.5-desktop-amd64. As I was not able to copy / paste from my pc (Windows 10) with Ctrl+Alt+C / Ctrl+Alt+V (and even Ctrl+C/Ctrl+V, I was going to install and enalble Guest Addition with

sudo apt install linux-headers-$(uname -r) build-essential dkms

but simply nothing happens! If I do Devices/Insert Guest Addition CD Image I get this error:

Virtualbox unable to insert the virtual optocal disk C:\ Program Files \ Oracle \ Virtualbox \ VBoxguestadditions.iso into the machine Xubuntu

Can someone help to solve this problem please? I already powered off the VM, I already rebooted it but nothing. In the Storage/Optical Drive I have VBoxGuestAdditions.iso even if I did not select it...no clue

Also in Devices/Optical Drivers the VBoxGuestAdditions.iso is checkmarked...

2 Answers

sudo apt install linux-headers-$(uname -r) build-essential dkms
has to be done in a terminal IN THE VM.
The current GuestAdditions.iso contains a set of commands that needs these installed.

If the ISO is already mounted (ticked in the settings), it cannot be inserted, giving the error you have.

Also if the ISO is present DURING BOOT, it will not Autostart.
Remove and Reinsert it using Virtualbox settings or menus - alternatively start a Terminal/Shell and launch the "autostart" script from there, it is present on the virtual disk created by the ISO.

If the GuestAddition CD is present in your optical disk (checkmarked) and the command
sudo apt install linux-headers-$(uname -r) build-essential dkms
has succeeded then execute the next commands
cd /media
cd <your_user_name>
cd VBox_Ga*
./autorun.sh
If the disk is not mounted, you can try to do it manually.
ls /dev/sr*
This will typically show /dev/sr0. Then:
sudo mkdir /media/<your_user_name>/ANameToChooseForTheDisk
sudo mount /dev/sr0 /media/<your_user_name>/ANameToChooseForTheDisk
If the mount succeeds (read-only) the contents of the disk show up in ANameToChooseForTheDisk and you can run the ./autorun.sh from there.