POSIX

Last updated

Portable Operating System Interface (IEEE 1003)
AbbreviationPOSIX
StatusPublished
Year started1988;38 years ago (1988)
Latest versionIEEE Std 1003.1-2024
2024;2 years ago (2024)
Organization Austin Group (IEEE Computer Society, The Open Group, ISO/IEC JTC 1/SC 22/WG 15)
Related standards ISO/IEC 9945
Domain Application programming interfaces
Website posix.opengroup.org

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. [1] [2]

Contents

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] [ further explanation needed ]

Name

The standards emerged from a project that began in 1984 building on work from related activity in the /usr/group association. [5] Richard Stallman suggested the name POSIX to the IEEE [6] [7] instead of the former IEEE-IX. [8] The committee found it more easily pronounceable and memorable, and thus adopted it.[ citation needed ]

Originally, POSIX referred to IEEE Std 1003.1-1988, released in 1988. The family of POSIX standards is formally designated as IEEE 1003 and the ISO/IEC standard number is ISO/IEC 9945.

POSIX is a trademark of the IEEE. [1]

Versions

POSIX originally consisted of a single document for core services but over time additional documents were published to extend and revise the specification. Before 1997, POSIX comprised multiple documents that were published over the course of several years. After 1997, the Austin Group produces specifications titled Single UNIX Specification (SUS). Over time, the group publishes versions of this specification and later POSIX is amended per some or all of a SUS version. A SUS version consists of a collection of volumes – each for a grouping of required behavior – plus other information (outside of a volume). [9] Each volume is assigned an issue number that is the same for each volume of a version, but is not the same value as the version. For example, SUS version 3 (SUSv3) includes volumes labeled issue 6.

As of 2014, POSIX documentation is divided into two parts:

Before 1997

POSIX.1

Core Services (IEEE Std 1003.1-1988) incorporates standard ANSI C and includes:

Process Creation and Control
Signals
Floating Point Exceptions
Segmentation / Memory Violations
Illegal Instructions
Bus Errors
Timers
File and Directory Operations
Pipes
C Library (Standard C)
The POSIX terminal interface

POSIX.1b

Real-time extensions (IEEE Std 1003.1b-1993, later appearing as librt—the Realtime Extensions library) includes: [11]

Priority Scheduling
Real-Time Signals
Clocks and Timers
Semaphores
Message Passing
Shared Memory
Asynchronous and Synchronous I/O
Memory Locking Interface

POSIX.1c

Threads extensions (IEEE Std 1003.1c-1995) includes:

Thread Creation, Control, and Cleanup
Thread Scheduling
Thread Synchronization
Signal Handling

POSIX.2

Shell and Utilities (IEEE Std 1003.2-1992) includes:

Command Interpreter
Utility Programs

POSIX.1-2001

POSIX.1-2001 (IEEE Std 1003.1-2001) consists of most of SUSv3 which consists of volumes (issue 6): Base Definitions, System Interfaces and Headers, and Commands and Utilities. The POSIX specification specifically excludes the SUSv3 requirements for a curses API (often called X/Open Curses, even though there is no distinct grouping of this in SUSv3). [12]

IEEE Std 1003.1-2004 modifies POSIX.1-2001 via two minor updates or errata referred to as technical corrigenda documents. [13] [14]

POSIX.1-2008

Similar to its predecessor, POSIX.1-2008 (IEEE Std 1003.1-2008, 2016 Edition) consists of most of the normative material of SUSv4 (issue 7 of volumes Base Definitions, System Interfaces and Headers, Commands and Utilities). [15] SUSv4 also includes rationale information that largely applies to POSIX although not included per se.

POSIX.1-2017

POSIX.1-2017 (IEEE Std 1003.1-2017) revises the previous version (POSIX.1-2008) via two technical corrigenda. [16]

POSIX.1-2024

POSIX.1-2024 (IEEE Std 1003.1-2024) was published on 14 June 2024. [15] [17]

As of POSIX 2024, the standard is aligned with the C17 language standard.

Controversies

512- vs 1024-byte blocks

POSIX mandates 512-byte default block sizes for the df and du utilities, reflecting the typical size of blocks on disks. When Richard Stallman and the GNU team were implementing POSIX for the GNU operating system, they objected to this on the grounds that most people think in terms of 1024 byte (or 1 KiB) blocks. The environment variable POSIX_ME_HARDER was introduced to allow the user to force the standards-compliant behaviour. [18] The variable name was later changed to POSIXLY_CORRECT. [19] As of 2025, this variable is also used for a number of other behaviour quirks. [20] [21] [22] [23] [24] [25] [26] [27] [28]

Conformance

An operating system can be classified depending upon the degree of conformance with a POSIX standard.

Certified

Current versions of the following operating systems have been certified to conform to one or more of the various POSIX standards. This means that they passed the automated conformance tests [29] and their certification has not expired and the operating system has not been discontinued. [30] [31]

Formerly certified

Some versions of the following operating systems had been certified to conform to one or more of the various POSIX standards. This means that they passed the automated conformance tests. The certification has expired and some of the operating systems have been discontinued. [30]

Partially conformant

The following are not certified as POSIX conforming yet are considered partially conforming which is sometimes called compliant:[ citation needed ]

Partially conformant via compatibility layer

The following operating systems are not certified as POSIX conformant, but they conform in large part to the standard by implementing POSIX support via a compatibility feature (usually translation libraries, or a layer atop the kernel).

Conformance via subsystem

Some technologies allow an operating system to enjoy a level of conformance to POSIX even though the operating system itself has little or no conformance.

For Windows

Although Windows does not conform to POSIX, the following technologies provide a level of compliance.

Cygwin
Provides a largely POSIX-compliant development and run-time environment for Microsoft Windows.
MinGW
A fork of Cygwin, provides a less POSIX-compliant development environment and supports compatible C-programmed applications via Msvcrt, Microsoft's old Visual C runtime library.
libunistd
A largely POSIX-compliant development library originally created to build the Linux-based C/C++ source code of CinePaint as is in Microsoft Visual Studio. A lightweight implementation that has POSIX-compatible header files that map POSIX APIs to call their Windows API counterparts. [61]
Microsoft POSIX subsystem
An optional Windows subsystem included in Windows NT-based operating systems up to Windows 2000. It supported POSIX.1 as it stood in the 1990 revision, without threads or sockets.
Interix
originally OpenNT by Softway Systems, Inc., is an upgrade and replacement for Microsoft POSIX subsystem that was purchased by Microsoft in 1999. It was initially marketed as a stand-alone add-on product and then later included as a component in Windows Services for UNIX (SFU) and finally incorporated as a component in Windows Server 2003 R2 and later Windows OS releases under the name "Subsystem for UNIX-based Applications" (SUA), later made deprecated in 2012 (Windows 8) [62] and dropped in 2013 (2012 R2, 8.1). It enables full POSIX compliance for certain Microsoft Windows products.[ citation needed ]
Windows Subsystem for Linux (WSL)
A compatibility layer for running Linux binary executables natively on Windows 10 and 11 using a Linux image such as Ubuntu, Debian, or OpenSUSE among others, acting as an upgrade and replacement for Windows Services for UNIX. It was released in beta in April 2016. The first distribution available was Ubuntu.
UWIN
From AT&T Research implements a POSIX layer on top of the Win32 APIs.
MKS Toolkit
Originally created for MS-DOS, is a software package produced and maintained by MKS Inc. that provides a Unix-like environment for scripting, connectivity and porting Unix and Linux software to both 32- and 64-bit Microsoft Windows systems. A subset of it was included in the first release of Windows Services for UNIX (SFU) in 1998. [63] [64]
Windows C Runtime Library and Windows Sockets API
Implement commonly used POSIX API functions for file, time, environment, and socket access, [65] although the support remains largely incomplete and not fully interoperable with POSIX-compliant implementations. [66] [67] [ discuss ]

For OS/2

POSIX environments for OS/2:

emx+gcc
Largely POSIX compliant.

For DOS

POSIX environments for DOS include:

emx+gcc
Largely POSIX compliant
DJGPP
Partially POSIX compliant
DR-DOS
Multitasking core via EMM386 /MULTI – a POSIX threads frontend API extension is available

See also

References

  1. 1 2 3 4 "POSIX.1 FAQ". The Open Group. 13 June 2020. Retrieved 20 February 2023.
  2. ↑ "IEEE 1003.1-2024". IEEE Standards Association.
  3. ↑ "Shell Command Language - The Open Group Base Specifications Issue 7, 2013 Edition" . Retrieved 28 April 2020.
  4. ↑ "Introduction". The Open Group Base Specifications Issue 7, 2018 edition. Retrieved 22 July 2021.
  5. ↑ "JimIsaak - POSIX Impact". sites.google.com. Retrieved 15 September 2022.
  6. ↑ "A Backgrounder on IEEE Std 1003.1". Footnotes.
  7. ↑ "The origin of the name POSIX". stallman.org. Retrieved 26 September 2024.
  8. ↑ Stoughton, Nicholas. "An Update On Standards". ;login: .
  9. ↑ PASC Status (including POSIX) (Report). IEEE Computer Society. 4 December 2003. Retrieved 26 September 2024.
  10. ↑ "Test Suites VSX-PCTS2003". The Open Group.
  11. ↑ "librt(3LIB)". docs.oracle.com. man pages section 3: Library Interfaces and Headers. Oracle Corporation. 4 August 1998. Retrieved 18 February 2016. librt, libposix4- POSIX.1b Realtime Extensions library [...] librt is the preferred name for this library. The name libposix4 is maintained for backward compatibility and should be avoided. Functions in this library provide most of the interfaces specified by the POSIX.1b Realtime Extension.
  12. ↑ "The Single UNIX Specification Version 3 - Overview". unix.org.
  13. ↑ "IEEE Std 1003.1" (2004 ed.). Unix.org. Retrieved 26 July 2009.
  14. ↑ "Base Specifications, Issue 6" (2004 ed.). The Open Group. Retrieved 20 July 2024..
  15. 1 2 "The Austin Common Standards Revision Group". The Open Group. Retrieved 20 July 2024.
  16. ↑ "Base Specifications, Issue 7, 2018 Edition" (2018 ed.). The Open Group. Retrieved 20 July 2024.
  17. ↑ "Base Specifications, Issue 8" (2024 ed.). The Open Group..
  18. ↑ Stallman, Richard (28 August 1991). "Democracy Triumphs in Disk Units". Newsgroup:  gnu.announce. Usenet:   9108281809.AA03552@mole.gnu.ai.mit.edu – via Google Groups.
  19. ↑ "GNU Coding Standards". GNU.
  20. ↑ "environ(7) — Linux manual page". man7.org. Michael Kerrisk. 17 May 2025. Retrieved 10 October 2025.
  21. ↑ "bash(1) — Linux manual page". man7.org. Michael Kerrisk. 7 April 2025. Retrieved 10 October 2025.
  22. ↑ "file(1) — Linux manual page". man7.org. Michael Kerrisk. 17 June 2025. Retrieved 10 October 2025.
  23. ↑ "find(1) — Linux manual page". man7.org. Michael Kerrisk. 9 July 2025. Retrieved 10 October 2025.
  24. ↑ "grep(1) — Linux manual page". man7.org. Michael Kerrisk. 21 March 2025. Retrieved 10 October 2025.
  25. ↑ "more(1) — Linux manual page". man7.org. Michael Kerrisk. 9 August 2025. Retrieved 10 October 2025.
  26. ↑ "patch(1) — Linux manual page". man7.org. Michael Kerrisk. 1 May 2025. Retrieved 10 October 2025.
  27. ↑ "ps(1) — Linux manual page". man7.org. Michael Kerrisk. 23 April 2025. Retrieved 10 October 2025.
  28. ↑ "renice(1) — Linux manual page". man7.org. Michael Kerrisk. 9 August 2025. Retrieved 10 October 2025.
  29. ↑ "POSIX Certified by IEEE and The Open Group - Program Guide". Section 2, How to Achieve Certification. Retrieved 26 September 2024.
  30. 1 2 "POSIX Certified by IEEE and The Open Group - Program Guide". Section 4, Renewals and Certified Product Updates. Retrieved 26 September 2024.
  31. ↑ "Certified Products by Company". The Open Group. n.d. Retrieved 22 January 2022.
  32. 1 2 "IBM". The Open Group. Retrieved 23 January 2022.
  33. ↑ "Hewlett-Packard". The Open Group. Retrieved 26 January 2014.
  34. 1 2 "POSIX Certification Register". The Open Group . Retrieved 22 August 2024.
  35. ↑ "macOS version 10.5 Leopard on Intel-based Mac computers". Register of Open Branded Products. The Open Group. Retrieved 20 May 2015.
  36. ↑ "macOS version 26.0 Tahoe on Intel-based Mac computers". The Open Group. Retrieved 5 October 2025.
  37. ↑ "macOS version 26.0 Tahoe on Apple Silicon-based Mac computers". The Open Group. Retrieved 5 October 2025.
  38. ↑ "SCO OpenServer Release 5". The Open Group. 3 May 1995. Retrieved 24 December 2021.
  39. ↑ "UnixWare ® 7.1.3 and later". The Open Group. 16 May 2003. Retrieved 24 December 2021.
  40. ↑ "Huawei Technology Co., Ltd". The Open Group. Retrieved 26 May 2017.
  41. ↑ "Inspur Co., Ltd". The Open Group. Retrieved 26 May 2017.
  42. ↑ "Silicon Graphics, Inc". The Open Group. Retrieved 26 January 2014.
  43. ↑ "The Open Brand - Register of Certified Products". Open Group. 23 July 2003. Archived from the original on 2 August 2003. Retrieved 23 January 2022.
  44. ↑ "QNX Achieves New POSIX Certification" (Press release). QNX. 8 April 2008. Retrieved 16 January 2016.
  45. ↑ "Oracle Corporation". The Open Group. Archived from the original on 12 July 2017. Retrieved 26 January 2014.
  46. ↑ "Hewlett-Packard". The Open Group. Archived from the original on 9 July 2014. Retrieved 26 January 2014.
  47. ↑ "Huawei LiteOS / LiteOS". Gitee. Huawei. Retrieved 23 May 2024.
  48. ↑ Schweikhardt, Jens. "FreeBSD POSIX 2001 Utility Compliance". FreeBSD.
  49. ↑ Mark Halper (7 November 1994). "HP 3000 sales catch market by surprise". Computerworld. Vol. 28, no. 4. IDG Enterprise.
  50. ↑ Solter, Nicholas A.; Jelinek, Jerry; Miner, David (21 March 2011). OpenSolaris Bible. John Wiley & Sons. ISBN   9781118080313.
  51. ↑ Lamie, Bill; Taubinger, Rafael (15 June 2023). "RTOS with standard POSIX pthreads API: a complement to embedded Linux". Embedded.com. Retrieved 13 September 2023.
  52. ↑ "OpenVOS POSIX.1: Conformance Guide". Status Technologies. Retrieved 26 November 2021.
  53. ↑ ULTRIX POSIX Conformance Document (PDF). Digital. June 1990. Retrieved 13 December 2021.
  54. ↑ "POSIX Support". Zephyr documentation. Retrieved 7 March 2023.
  55. ↑ "Aminet - dev/C/Vbcc_PosixLib.lha".
  56. ↑ "Programming IBM PASE for i" (PDF). ibm.com. IBM. 2013. Retrieved 25 November 2021.
  57. ↑ "FIPS 151-2 Conformance Validated Products List". Perennial Test Lab. Retrieved 14 August 2022.
  58. ↑ "APE — ANSI/POSIX Environment". Plan 9 documents. Bell Labs. Archived from the original on 1 June 2017.
  59. ↑ Realtime Products Technical Summary, Fifth Edition (PDF). Digital Equipment Corporation. December 1992. Retrieved 8 December 2021.
  60. ↑ "Chapter 29 - POSIX Compatibility". MS Windows NT Workstation Resource Kit. Microsoft. Archived from the original on 15 January 2008.
  61. ↑ Rowe, Robin (8 September 2022). "libunistd". Github. Retrieved 18 February 2023. If you want to build single codebase C++ code to run on Windows, Linux and MacOS, you need this for Windows
  62. ↑ "Features Removed or Deprecated in Windows Server 2012". Microsoft Docs . 31 August 2016.
  63. ↑ "Windows NT Services for UNIX Add-On Pack". Microsoft . Archived from the original on 8 May 1999.
  64. ↑ "MKS Solves Enterprise Interoperability Challenges" (Press release). Archived from the original on 28 April 1999.
  65. ↑ "Deprecated CRT Functions". Microsoft Docs . 15 October 2009. Retrieved 23 July 2022.
  66. ↑ "Porting Socket Applications to Winsock". Microsoft Docs . 7 January 2021. Retrieved 23 July 2022.
  67. ↑ "Winsock Programmer's FAQ Articles: BSD Sockets Compatibility". Warren Young. 31 August 2015. Retrieved 8 October 2015.
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