POSIXStandards

POSIX standards are a family of specifications intended to promote portability of software across Unix-like operating systems. They define a common set of application programming interfaces (APIs), command-line utilities, and behavioral expectations that allow programs to be compiled and run on different systems with predictable results. The standards are widely referred to as POSIX, and they are maintained through a collaboration involving IEEE, The Open Group, and ISO/IEC.

The POSIX suite is organized into parts that cover different aspects of system interfaces. POSIX.1 specifies the core C library APIs, process control, I/O operations, signals, and related facilities. POSIX.2 defines the behavior and syntax of many shell utilities and scripting interfaces. POSIX.4 addresses real-time extensions, including timers, clocks, and scheduling mechanisms. In addition to the core standards, The Open Group maintains The Open Group Base Specifications, which function as a practical reference implementation and compatibility baseline for POSIX interfaces. ISO/IEC 9945 is the ISO/IEC formalization of the same family, aligning national standards with the IEEE specifications.

History and governance: POSIX originated in the 1980s as an effort to standardize Unix interfaces and promote software portability. IEEE played a leading role in early development, with later formalization and maintenance by The Open Group and international standardization through ISO/IEC 9945. Compliance is demonstrated through conformance test suites published by The Open Group and other bodies, and many vendors claim POSIX compatibility for their operating systems.

Impact and scope: Most modern Unix-like systems, including Linux, macOS, and BSD derivatives, implement substantial portions of POSIX. While POSIX compatibility supports portability, implementations may vary in non-POSIX extensions and optional features. Windows environments offer partial POSIX support through compatibility layers and subsystem projects. See also POSIX.1, POSIX.2, The Open Group, IEEE 1003, ISO/IEC 9945, Unix.