Linux PRE-EMPT & EtherCAT

can you explain with more detail ?
I want to make a 5 axis cnc software for my customer. However, i will design new ui. also i will add new things that not include in standard ui of linuxcnc and i dont want my customer to know i am using the linuxcnc. Also i dont want to share the codes?
This all considerations is not possible? İf it is possible, what can i do?

I think the best answer I can give is to read the licenses in the copying and copying.more files that ship with Linuxcnc 
copying.more is here github.com/LinuxCNC/linuxcnc

There appear to be provisions there that would allow what you want to do if you go about it the right way. Take your own advice on it.

There are many commercial machines or hardware devices that use open source software. eg  a Netgear or Dlink router comes to mind.