Ubuntu的root用户

The root account is disabled when you first install Ubuntu. The first user created during the installation has administrative rights on the system, and can run programs as root with sudo, using only their normal user password. For example: sudo apt-get update.
If you wish to use the root account in more traditional UNIX fashion, you can set the root password by typing sudo passwd root. This will allow you to use su or login as root on the console.
If you need a shell with root privileges, run sudo -s.
All uses of sudo will require the user's password.