How to disable the System Integrity Protection of a iMac
Apple introduced the System Integrity Protection (rootless) mode as a security feature as of OS X El Capitan. It prevents you (and programs) from changing root-level files even with your password, but it can stop some programs from working. Here's how you can disable it:
csrutil enable.
After that reboot your system and it should be disabled. To check if it is disable you can open a terminal and type:
csrutil status
That's all!
Enjoy,
Your ArtIT Team