In the Terminal you must first login as root/superuser.
1. In the Terminal type
- Code: Select all
and press return.
2. Type in the password of the administrator account of your Mac and press return (you don't see an indication that you are typing your password).
Now you are logged in as superuser and you can enter the command you posted. Be careful though with typing in commands in the Terminal when you are logged in as superuser, because if you don't know what you're doing you can seriously damage your system (for example, there is a command to remove files without a warning).