Lesson 4.3: Changing users: su and sudo

Why you work as an ordinary user, how sudo runs a single command as root (and logs it), sudo -l, -u and -i, why su to root fails on Ubuntu, and the principle of least privilege.

16 min

You will learn to

Explain why daily work is done as an ordinary user
Run single commands as root with sudo and see what you're allowed with sudo -l
Open and leave a root shell with sudo -i and exit
Run a command as another user with sudo -u
Find sudo usage in /var/log/auth.log

Key terms

Privilege: The right to do something the system protects: read other users' files, install software, change settings.
Principle of least privilege: Give every user and program only the rights it needs, only for as long as it needs them.
sudo: Runs a single command as another user, root by default, after asking for your own password. Who may run what is set in /etc/sudoers, and every use is logged.
su: Starts a new shell as another user after asking for that user's password. su - also loads that user's login environment.
Root shell: A shell running as root, recognisable by the # prompt. Opened with sudo -i or sudo su -, closed with exit.
Authentication log: /var/log/auth.log: logins, failed passwords and every sudo command, with time, user and command.

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