Users and Groups

Linux is a native multi-accessible system.

Enable and disable root

sudo password root
sudo passwd -l root

To open a shell with root, just

su

Add a new group bar

sudo groupadd bar

Add a new user foo to a group bar

sudo useradd -G bar foo

Add an existing user foo to a group bar

sudo usermod -a -G bar foo

Print current settings

id bar
groups foo