VirtualBox shared folder doesn't mount

Help
1

I have Linux Mint Mate insttalled as a virtual machine in VirtualBox. I specified a folder in Settings > Shared Folders as Read-only and Automount.

The VM starts and runs with no visible error, but the shared folder is not mounted. What am I missing?

NixOS is installed on an Intel i5-11600K with 16 GB memory using the integrated GPU. Secure Boot is disabled.

VirtualBox configuration:

Allow unfree packages

nixpkgs.config.allowUnfree = true;

VirtualBox configuration

virtualisation.virtualbox = {
host = {
enable = true;
enableExtensionPack = true;
};
guest = {
enable = true;
draganddrop = true;
};
};

System:

$ nix-shell -p nix-info --run “nix-info -m”
system: "x86_64-linux"
host os: Linux 6.6.47, NixOS, 24.05 (Uakari), 24.05.4248.2527da1ef492
multi-user?: yes
sandbox: yes
version: nix-env (Nix) 2.18.5
channels(root): "nixos-24.05"
nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

2

What I was missing is that the user in the VM has to be a member of the vboxsf group.

3

sudo usermod -a -G vboxsf

Doesn’t work for me. The shared folder is still only accessible via root. Checked /etc/group it’s definition is there. Guess, I’m missing something else in the NixOS/Nix configuration.