Error: (sudo: unable to change to root gid: Operation not permitted)

Question

I have installed Oracle VirtualBox on my Windows 10 machine. As a guest OS I installed Ubuntu 16.04.04.

When I open the terminal on Ubuntu and run a command like:

sudo apt-get update

I get the following errors:

sudo: unable to change to root gid: Operation not permitted
sudo: unable to initialize policy plugin

Actually I can't execute any sudo command. Any one knows how to diagnose/solve the problem?

I should metion that I am logged in using the guest account. So when I enter groups I get

guest-rqj3wa

Solution

This is the normal behavior of guest account. it's not permitted for guest account to run commands like su or sudo because of security concerns. Otherwise anyone could sit behind your desk and do whatever he wanted to your system like installing/removing anything.

And remember that when you are logged in as a normal user, to run sudo you have to be a member of "sudo" group.