1. Groups
    • create new group:
      sudo groupadd groupname
  2. Users
    • add existing user into group:
      sudo usermode -G groupname username
    • remove user from group:
      sudo deluser username groupname
    • show groups user belongs into:
      groups username
    • show all users belonging into some group:
      sudo cat /etc/group|grep groupname
      members groupname