I had initiated what became a long series of messages re failure of nmap, and failure of other basic system commands on a refurb Dell Optiplex 780 computer obtained from Discount Electronics. It turns out that this computer--maybe all Dells of that 8-year-old vintage--contains a setup system which defines the way that the computer can be used, regarding bootup source, and various things, some of which are not visible, having been deliberately hidden by that very same setup function. This was probably a reasonable approach for the commercial office use it was refurbed from. It is designed to keep a user from messing with the way the computer performed. A lot of features which are visible during boot are not reachable by any means, at least by me, and apparently by a man named Joe at Discount Electronics. The computer even has a means of applying a padlock so that it cannot be opened up by a user! During an interchange with Joe, I told him that unless he can tell me how to remove the nanny functions, I would return the computer for refund. He told me that the company does not take back units for refund, only for the sale of a newer computer. This was to be only an interim machine, since all my computers were damaged by lightning. Now I will return it to Windows and donate it. I am fortunately financially able to do that. But I am writing to warn anyone contemplating a purchase from Discount Electronics, DON'T! If you intend to run Linux--as I'm sure all readers here do--then don't purchase from Discount Electronics. And make sure you get a written promise that you will be allowed to return for refund if the machine you purchase (somewhere else!) is not suitable. (For myself, I have come up with an HP laptop on which I will try and run Linux--HP says no problem, but I haven't tried it yet. I have to say that for a machine that originally ran Windows 7, it is impressive with Win 10 on it.) --doug