I installed Ubuntu Core using these instructions, and added a user. But when I try to add the user to the admin group, it says the group does not exist. What do I do?
PS I had to install
sudo, however it made no difference.
On traditional Linux/Unix systems there is no "admin" group, such group was widely introduced for desktop usage. If you really need an admin group on a core system (you may not needed), you will need to create it manually: