Troubles with permissions

[Goffraiden]

I need to add my user (root) to the staff group, but when I try with
usermod -G staff root
i get the following error message:
usermod: error opening shadow group file

How can I add users to this group?

[Stephen]

I need to add my user (root) to the staff group, but when I try with
usermod -G staff root
i get the following error message:
usermod: error opening shadow group file

How can I add users to this group?

adduser root staff will add root to the staff group you will have to logout of your current shell and back in for it to take effect.