You have that Linux desktop or server precisely how you want it and are interested in either creating a spot-on backup or a live ISO that you can then install on other (similar) hardware. How do you do it? You could go through the process of learning a number of commands to take care of the process, or you could install and use a handy tool called Systemback.
The Systemback tool allows you to create restore points, backups, and live images of a running system. Currently, it only works for Ubuntu derivatives based on 14.04, 14.10, and 15.04. It does, however, work like a champ (and does so quite easily).