How do I disable System Integrity Protection (SIP) AKA "rootless" on macOs [OS X]
Apple's documentation covers disabling SIP, About System Integrity Protection on your Mac and Configuring System Integrity Protection.

An article on lifehacker.com lists these steps:


  
  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.
  


You can verify whether a file or folder is restricted by issuing this ls command using the capital O (and not zero 0) to modify the long listing flag:

ls -lO /System /usr 


Look for the restricted text to indicate where SIP is enforced. 

By default (=SIP enabled), the following folders are restricted (see Apple Support page):

/System
/usr
/bin
/sbin
Apps that are pre-installed with OS X


... and the following folders are free:

/Applications
/Library
/usr/local