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POSIX ○˒｜Definition｜1st｜20251119205401-00-⌔
POSIX
The Portable Operating System Interface (POSIX; IPA: /ˈpɒz.ɪks/1) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems.1 In order to define a level of compatibility, POSIX specifies many aspects of functionality that can be classified as application programming interface (API), command-line shell, and shell commands. Originally derived from commonly-found Unix APIs, shells, and commands (partly because Unix was considered manufacturer-neutral), today many systems conform to the standard – including branded Unix systems, Unix-like systems, and many systems that were historically unrelated to Unix.12
The standardized user command line and scripting interface were based on the UNIX System V Bourne shell.3 Many user-level programs, services, and utilities (including awk, echo, ed) were also standardized, based on UNIX System V versions of them, along with required program-level services (including basic I/O: file, terminal, and network). POSIX also defines a standard threading library API which is supported by most modern operating systems.
The POSIX standard is developed by the Austin Group (a joint working group among the IEEE, The Open Group, and the ISO/IEC JTC 1/SC 22/WG 15).
POSIX is intended to be used by both application and system developers.4
Printed 2026-06-28.
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Link to original Footnotes
“POSIX.1 FAQ”. The Open Group. 13 June 2020. Retrieved 20 February 2023. ↩ ↩2 ↩3
“IEEE 1003.1-2024”. IEEE Standards Association. ↩
“Shell Command Language - The Open Group Base Specifications Issue 7, 2013 Edition”. Retrieved 28 April 2020. ↩
“Introduction”. The Open Group Base Specifications Issue 7, 2018 edition. Retrieved 22 July 2021. ↩
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