At the beginning I would like to explain the appearance of the word "command" in this publication. It reflects the same one real bad message. Saying "command" we mean a certain order, some instructions. I say "running" in the publication, I mean the program you want. Linux is not 'famous' dos. Here, everything is separate, ie, at any time, you can even remove the corresponding files on the move! However, it is difficult to use the concept of "program", which can make you uncomfortable. So, I will continue to use the term "command", but you must remember - this is not a Linux!