POSIX

Template:Short description Template:Distinguish Template:Use dmy dates Template:Infobox technology standard The Portable Operating System Interface (POSIX; Template:IPAc-en<ref name="FAQ">Template:Cite web</ref>) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems.<ref name="FAQ"/> POSIX defines application programming interfaces (APIs), along with command line shells and utility interfaces, for software compatibility (portability) with variants of Unix and other operating systems.<ref name="FAQ"/><ref name="IET">Template:Cite web</ref> POSIX is also a trademark of the IEEE.<ref name="FAQ"/> POSIX is intended to be used by both application and system developers.<ref>Template:Cite web</ref> As of POSIX 2024, the standard is aligned with the C17 language standard.

Name

Originally, the name "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.

The standards emerged from a project that began in 1984 building on work from related activity in the /usr/group association.<ref>Template:Cite web</ref> Richard Stallman suggested the name POSIX to the IEEE<ref>Template:Cite web</ref><ref>Template:Cite web</ref> instead of the former IEEE-IX.<ref>Template:Cite journal</ref> The committee found it more easily pronounceable and memorable, and thus adopted it.Template:Cn

Overview

Unix was selected as the basis for a standard system interface partly because it was "manufacturer-neutral". However, several major versions of Unix existed—so there was a need to develop a common-denominator system. The POSIX specifications for Unix-like operating systems originally consisted of a single document for the core programming interface, but eventually grew to 19 separate documents (POSIX.1, POSIX.2, etc.).<ref>Template:Cite report</ref> The standardized user command line and scripting interface were based on the UNIX System V shell.<ref>Template:Cite web</ref> Many user-level programs, services, and utilities (including awk, echo, ed) were also standardized, 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. In 2008, most parts of POSIX were combined into a single standard (IEEE Std 1003.1-2008, also known as POSIX.1-2008).

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

• POSIX.1, 2013 Edition: POSIX Base Definitions, System Interfaces, and Commands and Utilities (which include POSIX.1, extensions for POSIX.1, Real-time Services, Threads Interface, Real-time Extensions, Security Interface, Network File Access and Network Process-to-Process Communications, User Portability Extensions, Corrections and Extensions, Protection and Control Utilities and Batch System Utilities. This is POSIX 1003.1-2008 with Technical Corrigendum 1.)
• POSIX Conformance Testing: A test suite for POSIX accompanies the standard: VSX-PCTS or the VSX POSIX Conformance Test Suite.<ref name = "VSX-PCTS">Template:Cite web</ref>

The development of the POSIX standard takes place in the Austin Group (a joint working group among the IEEE, The Open Group, and the ISO/IEC JTC 1/SC 22/WG 15).

Versions

Parts before 1997

Before 1997, POSIX comprised several standards:

• POSIX.1: Core Services (incorporates Standard ANSI C) (IEEE Std 1003.1-1988)
  • 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)<ref>

Template:Cite web</ref>

• • 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)
  • Thread Creation, Control, and Cleanup
  • Thread Scheduling
  • Thread Synchronization
  • Signal Handling
• POSIX.2: Shell and Utilities (IEEE Std 1003.2-1992)
  • Command Interpreter
  • Utility Programs

Versions after 1997

After 1997, the Austin Group developed the POSIX revisions. The specifications are known under the name Single UNIX Specification, before they become a POSIX standard when formally approved by the ISO.

POSIX.1-2001 (with two TCs)

POSIX.1-2001 (or IEEE Std 1003.1-2001) equates to the Single UNIX Specification, version 3 minus X/Open Curses.<ref>Template:Cite web</ref>

This standard consisted of:

• the Base Definitions, Issue 6,
• the System Interfaces and Headers, Issue 6,
• the Commands and Utilities, Issue 6.

IEEE Std 1003.1-2004 involved a minor update of POSIX.1-2001. It incorporated two minor updates or errata referred to as Technical Corrigenda (TCs).<ref>Template:Cite web</ref> Its contents are available on the web.<ref>Template:Cite web.</ref>

POSIX.1-2008 (with two TCs)

Base Specifications, Issue 7 (or IEEE Std 1003.1-2008, 2016 Edition).<ref name=AustinGroup>Template:Cite web</ref>

This standard consists of:

• the Base Definitions, Issue 7,
• the System Interfaces and Headers, Issue 7,
• the Commands and Utilities, Issue 7,
• the Rationale volume.

POSIX.1-2017

IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008) - IEEE Standard for Information Technology—Portable Operating System Interface (POSIX(R)) Base Specifications, Issue 7 is available from either The Open Group or IEEE. It is technically identical to POSIX.1-2008 with Technical Corrigenda 1 and 2 applied. Its contents are available on the web.<ref>Template:Cite web</ref>

POSIX.1-2024

IEEE Std 1003.1-2024 - IEEE Standard for Information Technology—Portable Operating System Interface (POSIX(R)) Base Specifications, Issue 8 was published on 14 June 2024.<ref name=AustinGroup/> Its contents are available on the web.<ref>Template:Cite web.</ref>

Controversies

512- vs 1024-byte blocks

Template:Primary sources 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 Template:Tt was introduced to allow the user to force the standards-compliant behaviour.<ref>Template:Cite newsgroup</ref> The variable name was later changed to Template:Tt.<ref>Template:Cite web</ref> This variable is now also used for a number of other behaviour quirks.

POSIX-oriented operating systems

Depending upon the degree of compliance with the standards, one can classify operating systems as fully or partly POSIX compatible.

POSIX-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<ref name="achieve_status">Template:Cite web</ref> and their certification has not expired and the operating system has not been discontinued.<ref name="renew_certification">Template:Cite web</ref><ref>Template:Cite web</ref> Template:Div col

• AIX<ref name="ibm">Template:Cite web</ref>
• HP-UX<ref name="hp">Template:Cite web</ref>
• INTEGRITY<ref name="posix-register">Template:Cite web</ref>
• macOS (since Mac OS X Leopard<ref>Template:Cite web</ref> to macOS Sequoia<ref>Template:Cite web</ref><ref>Template:Cite web</ref>)
• OpenServer<ref>Template:Cite web</ref>
• UnixWare<ref>Template:Cite web</ref>
• VxWorks<ref name="posix-register"/>
• z/OS<ref name="ibm"/>

Formerly POSIX-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.<ref name="renew_certification" /> Template:Div col

• EulerOS (exp. 2022)<ref>Template:Cite web</ref>
• Inspur K-UX (exp. 2019)<ref>Template:Cite web</ref>
• IRIX (defunct 2006)<ref>Template:Cite web</ref>
• OS/390 (defunct 2004)<ref>Template:Cite web</ref>
• QNX Neutrino<ref>Template:Cite press release</ref>
• Solaris (exp. 2019)<ref>Template:Cite web</ref>
• Tru64 (defunct 2010)<ref>Template:Cite web</ref>
• LiteOS (defunct 2020)<ref>Template:Cite web</ref>

Mostly POSIX-compliant

The following are not certified as POSIX compliant yet comply in large part: Template:Div col

• Android (Available through Android NDK)Template:Citation needed
• Darwin (core of macOS and iOS)
• DragonFly BSD
• FreeBSD<ref name="FreeBSD">Template:Cite web</ref>
• Haiku
• illumos
• Linux (most distributions)
• LynxOS
• Minix (now Minix 3)
• MPE/iX<ref>Template:Cite magazine</ref>
• NetBSD
• Nucleus RTOS
• NuttX
• OpenBSD
• OpenSolaris<ref>Template:Cite book</ref>
• PikeOS RTOS for embedded systems with optional PSE51 and PSE52 partitions; see partition (mainframe)
• PX5 RTOS<ref>Template:Cite web</ref>
• Redox
• RTEMS – POSIX API support designed to IEEE Std. 1003.13-2003 PSE52
• SerenityOS
• Stratus OpenVOS<ref>Template:Cite web</ref>
• SkyOS (discontinued)
• Syllable (discontinued)
• ULTRIX<ref>Template:Cite manual</ref>
• VSTa
• VMware ESXi
• Xenix
• Zephyr<ref>Template:Cite web</ref>

POSIX for Microsoft Windows

• 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.<ref>Template:Cite web</ref>
• 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)<ref>Template:Cite web</ref> and dropped in 2013 (2012 R2, 8.1). It enables full POSIX compliance for certain Microsoft Windows products.Template:Citation needed
• Windows Subsystem for Linux, also known as WSL, is 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.<ref>Template:Cite web</ref><ref>Template:Cite press release</ref>
• Windows C Runtime Library and Windows Sockets API implement commonly used POSIX API functions for file, time, environment, and socket access,<ref>Template:Cite web</ref> although the support remains largely incomplete and not fully interoperable with POSIX-compliant implementations.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>Template:Discuss

POSIX for OS/2

Mostly POSIX compliant environments for OS/2:

• emx+gcc – largely POSIX compliant

POSIX for DOS

Partially POSIX compliant environments for DOS include:

• emx+gcc – largely POSIX compliant
• DJGPP – partially POSIX compliant
• DR-DOS multitasking core via Template:Mono – a POSIX threads frontend API extension is available

Compliant via compatibility layer

The following are not officially certified as POSIX compatible, but they conform in large part to the standards by implementing POSIX support via some sort of compatibility feature (usually translation libraries, or a layer atop the kernel). Without these features, they are usually non-compliant.

• AmigaOS (through the ixemul library or vbcc_PosixLib<ref>Template:Cite web</ref>)
• eCos – POSIX is part of the standard distribution, and used by many applications. 'external links' section below has more information.
• IBM i (through the PASE compatibility layer)<ref>Template:Cite web</ref>
• MorphOS (through the built-in ixemul library)
• OpenVMS (through optional POSIX package)<ref>Template:Cite web</ref>
• Plan 9 from Bell Labs APE - ANSI/POSIX Environment<ref name="APE">Template:Cite web</ref>
• RIOT (through optional POSIX module)
• Symbian OS with PIPS (PIPS Is POSIX on Symbian)
• VAXELN (partial support of 1003.1 and 1003.4 through the VAXELN POSIX runtime library)<ref>Template:Cite manual</ref>
• Windows NT kernel when using Microsoft SFU 3.5 or SUA
  • Windows 2000 Server or Professional with Service Pack 3 or later. To be POSIX compliant, one must activate optional features of Windows NT and Windows 2000 Server.<ref name="MS">Template:Cite web</ref>
  • Windows XP Professional with Service Pack 1 or later
  • Windows Server 2003
  • Windows Server 2008 and Ultimate and Enterprise versions of Windows Vista
  • Windows Server 2008 R2 and Ultimate and Enterprise versions of Windows 7
  • albeit deprecated, still available for Windows Server 2012 and Enterprise version of Windows 8

See also

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• Template:Annotated link Template:Endash set of characters which should be supported in any POSIX-compliant character set locale
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External links

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