macOS Sierra ships with a new security process referred to as SIP or System Integrity Protection also known as rootless it has been part of the macOS since OSX 10.11 El Capitan.
What this essentially does is protect certain system level directories from being changed, notably
(but not /usr/local).
The setting can be altered by users wishing to add, edit or delete certain files in these folders.
Disabling SIP in macOS
Reboot your Mac into Recovery Mode by rebooting and holding down ‘command’ + ‘r’.
Launch a Terminal session and enter
Re-enabling SIP in macOS
Boot into Recovery Mode again and this time
You can see the status of SIP or rootless at any time not in Recovery Mode by just a command in the Terminal