Root And Sudo
The root user in GNU/Linux is the user which has administrative access to your system. Normal users do not have this access for security reasons. However, Kubuntu does not include the root user. Instead, administrative access is given to individual users, who may use the "sudo" application to perform administrative tasks. The first user account you created on your system during installation will, by default, have access to sudo. You can restrict and enable sudo access to users with the Users and Groups application (see the section called "Users and Groups" for more information).
When you run an application that requires root privileges, sudo will ask you to input your normal user password. This ensures that rogue applications cannot damage your system, and serves as a reminder that you are about to perform administrative actions which require you to be careful!
To use sudo when using the command line, simply type "sudo" before the command you wish to run. Sudo will then prompt you for your password.
Sudo will remember your password for a set amount of time (15 minutes by default). This feature was designed to allow users to perform multiple administrative tasks without being asked for a password each time.