Linux Basics/User management (System administrator)

The system administrator (superuser) and its functions

• The most important user in Linux is: root
• UID: 0, GID: 0
• Root can access everything in the system!
• The „su” command:
  • Changing user and executing command:
  • For example, we can become user mary:
    • su mary
  • If we use dash, then we get the whole environment of mary:
    • su - mary
  • We can add a group with the sg command. For example, we can add info:
    • sg info
• Sudo command
  • With sudo command we can execute superuser commands. It asks the user's password, this is important because we don't want anybody to modify our system.
  • Ubuntu-based systems get root permissions only by sudo, root user doesn't get password.
  • We don't edit sudo's settings from directly the file. We use the following command instead: # visudo
  • Settings → in /etc/sudoers file
  • Syntax: <username> ALL=NOPASSWD: ALL Example: joska ALL=NOPASSWD: ALL
  • Without NOPASSWD it asks the given user's password.
  • Setting superuser permission: ALL=(ALL:ALL) ALL