permissions of a folder to change to use grunt

I know it must have been answered somewhere but I cannot find it.

I want to install Grunt in a project directory, on my computer, on a virtual volume (I am in dual boot with Windows, and the directory I am working on is on a third volume, not the Windows one).

When I try to install it there it constantly return errors and I cannot use Grunt, even though I am using sudo. It still returns :

npm ERR! code EPERM
(... plenty of other lines of npm ERR! ...))
npm ERR! Please try running this command again as root/Administrator.

Now when I try to do it with the same project but after having copied it in my /home/username volume-directory, then it works fine.

What should I do ?

Thanks!