virtualbox.org

I have a immutable VM. I have set that property as a user, so for that specific user, the VM is immutable. I also have some differencing disks which is based on the immutable VM.

What happens if I change the immutable VM as another user? Let us say I install some new software. Will all differencing disks see this change and work fine? Or, will the differencing disks malfunction because I changed the base immutable disk? They dont see the change and will be surprised and crash?

If you succeed in modifying the base (or any intermediate) in a difference chain then you corrupt all of the difference images that depend directly or indirectly on the modified file.

mpack wrote:If you succeed in modifying the base (or any intermediate) in a difference chain then you corrupt all of the difference images that depend directly or indirectly on the modified file.

Just to confirm, this means that I can not change the base VM? If I change the base VM, then my differencing disks might exhibit errors?

I think I was quite clear and explicit above. However, confirmed. You will corrupt the child image(s). Of course the effect of that corruption would depend on what had been modified. Besides the actual corruption, VirtualBox itself may(*) refuse to load a child image if it detects that an ancestor image has been modified (the VDI header contains a "modify-UUID" field whose purpose is to detect precisely that) - and may do this regardless of the seriousness of the corruption, which it has no way to know.

(*) I have not looked to see that VBox actually carries out this validation check. However those modification UUID fields clearly exist for this purpose, so past or future versions of VBox would be entitled to do this check even if it isn't done now.