Apple has introduced System Integrity Protection, also known as “rootless”, with OS X 10.11, El Capitan. This is a step for general protection against malware. But, to turn it off…
Reboot your Mac into Recovery Mode by restarting your computer and holding down Command+R until the Apple logo appears on your screen.
Click Utilities > Terminal.
In the Terminal window, type in csrutil disable and press Enter.
Restart your Mac.