Posix standards, 1995, pdf.tar.gz
IEEE 1003.0
IEEE 1003.1
IEEE 1003.1B
ISO/IEC 9945
POSIX
Wikipedia:
POSIX or \\\"Portable Operating System Interface\\\"[1] is the collective name of a family of related standards specified by the IEEE to define the application programming interface (API) for software compatible with variants of the Unix operating system.