System Integrity Protection or Rootless mode is a security feature of OS X El Capitan operating system by Apple Inc. It protects certain system processes, file and folders from being modified or tampered with by other processes even when executed by the root user or by a user with root privileges(sudo). Following are the the key concepts of System Integrity Protection. 1. System Locations Cannot Be Written To - System files can be modified only by system processes signed with Apple’s code signing identity. App processes should instead write to locations designated for third-party developers. The following directories can only be written to by the system: System-Only Locations ● /bin ● /sbin ● /usr ● /System In contrast, the following directories are available to any process: Locations Available to Developers ● /usr/local ● /Applications ● [~]/Library All directories in /usr except for /usr/local are