https://developer.apple.com/library/archive/documentation/Darwin/Conceptual/KernelProgramming/BSD/BSD.html https://developer.apple.com/library/archive/documenta

https://developer.apple.com/library/archive/documentation/Darwin/Conceptual/KernelProgramming/BSD/BSD.html https://developer.apple.com/library/archive/documentation/Da... “The BSD portion of the OS X kernel is derived primarily from FreeBSD, a version of 4.4BSD that...” https://wiki.freebsd.org/Myths https://wiki.freebsd.org/Myths “The two operating systems do share a lot of code, for example most userland utilities and the C library on OS X are derived from FreeBSD versions.”