The Ubuntu operating system is installed with powerful administration tools that enable you to reset authentication for the system. In Ubuntu, you can reset the authentication by resetting the password for your account. The password can be set in one of two ways -- through the Ubuntu GUI desktop or from the command line.
Reset Password from Ubuntu Desktop
Click the “System” option on the top toolbar in the Ubuntu desktop, and then click “Preferences.”
Click the “About Me” option in the Preferences menu. The account profile for your account opens.
Click the button labeled “Change Password.” The Change Password dialog box opens.
Type your existing password into the “Current Password” field, and then click “Authenticate.” The “New Password” and “Retype New Password” fields become active.
Type the desired new password into the “New Password” field, and then verify the password by retyping in the “Retype New Password” field.
Click the “Change Password” button. The password for your account is updated.
Reset Password from Command Line
Click the “Applications” option from the top toolbar in the Ubuntu desktop, and then click the “Accessories” option.
Click the “Terminal” option. The command line terminal opens.
Type “passwd” at the command prompt, and then press the “Enter” key. A prompt appears requesting the current password.
Type the existing password at the command prompt, and then press the “Enter” key. A prompt appears instructing you to enter the new password.
Type the new password at the command prompt, and press the “Enter” key. The verification prompt appears.
Retype the new password at the prompt, and then press the “Enter” key. A notification displays that the password has been successfully updated.