How to fix shared folder permissions in VirtualBox

For my SDR experiments, I installed Skywave Linux in a VirtualBox VM. To transfer IQ files, I needed a shared folder between the Linux guest and the windows host.

Skywave Linux running in VirtualBox

Long story short: To allow the user "andy" (in this case) access to the shared folder, he needs to be in the "vboxsf" group. To add that user to this group:

sudo usermod -G vboxsf -a andy

Works a treat.