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The PORTABLE OPERATING SYSTEM INTERFACE (POSIX) is a family of standards specified by the IEEE Computer Societyfor maintaining compatibility between operating systems . POSIXdefines the application programming interface (API), along with command line shells and utility interfaces, for software compatibility with variants of Unix
Unix
and other operating systems.

CONTENTS

* 1 Name * 2 Overview

* 3 Versions

* 3.1 Parts before 1997

* 3.2 Versions after 1997

* 3.2.1 POSIX.1-2001 * 3.2.2 POSIX.1-2004 (with two TCs) * 3.2.3 POSIX.1-2008 (with two TCs)

* 4 Controversies

* 4.1 512- vs 1024-byte blocks

* 5 POSIX-oriented operating systems

* 5.1 POSIX-certified

* 5.2 Mostly POSIX-compliant

* 5.2.1 POSIXfor Microsoft Windows
Microsoft Windows
* 5.2.2 POSIXfor OS/2
OS/2
* 5.2.3 POSIXfor DOS
DOS
* 5.2.4 Compliant via compatibility feature

* 6 See also * 7 References * 8 External links

NAME

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

The standards emerged from a project that began circa 1985. Richard Stallman suggested the name _POSIX_ to the IEEE instead of former _IEEE-IX_. The committee found it more easily pronounceable and memorable, and thus adopted it.

OVERVIEW

Unix
Unix
was selected as the basis for a standard system interface partly because it was "manufacturer-neutral." However, several major versions of Unix
Unix
existed—so there was a need to develop a common denominator system. The POSIXspecifications for Unix-like
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.). The standardized user command line and scripting interface were based on the UNIX System V
UNIX System V
shell. 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 ). POSIXalso defines a standard threading library API which is supported by most modern operating systems. In 2008, most parts of POSIXwere combined into a single standard _(IEEE Std 1003.1-2008_, also known as _POSIX.1-2008)._

As of 2014 , POSIXdocumentation is divided in two parts:

* POSIX.1, 2013 Edition: POSIXBase 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
File
Access and Network Process-to-Process Communications, User Portability Extensions, Corrections and Extensions, Protection and Control Utilities and Batch System Utilities. This is POSIX1003.1-2008 with Technical Corrigendum 1.) * POSIXConformance Testing: A test suite for POSIXaccompanies the standard: VSX-PCTS or the VSX POSIXCONFORMANCE TEST SUITE.

The development of the POSIXstandard takes place in the Austin Group (a joint working group linking the IEEE, The Open Groupand the ISO/IEC JTC 1 organizations).

VERSIONS

PARTS BEFORE 1997

Before 1997, POSIXcomprised 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
File
and Directory Operations * Pipes * C Library (Standard C) * I/O Port Interface and Control * Process Triggers

* POSIX.1B: Real-time extensions (IEEE Std 1003.1b-1993, later appearing as librt—the Realtime Extensions library) )

* 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 Groupdeveloped the POSIXrevisions. The specifications are known under the name Single UNIX Specification, before they become a POSIXstandard when formally approved by the ISO.

POSIX.1-2001

_POSIX.1-2001_ (or IEEE Std 1003.1-2001) equates to the _Single UNIX Specification version 3._

This standard consisted of:

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

POSIX.1-2004 (with Two TCs)

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_. Its contents are available on the web.

POSIX.1-2008 (with Two TCs)

As of 2017 , _Base Specifications, Issue 7_ (or _IEEE Std 1003.1-2008_, 2016 Edition) represents the current version. A free online copy is available.

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.

CONTROVERSIES

512- VS 1024-BYTE BLOCKS

POSIXmandates 512-byte default block sizes for the df and du utilities, reflecting the typical size of blocks on disks. When Richard Stallman
Richard Stallman
and the GNU
GNU
team were implementing POSIXfor 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 _POSIXLY_CORRECT_ was introduced to allow the user to force the standards-compliant behaviour. The variable name _POSIX_ME_HARDER_ was also discussed. The variable _POSIXLY_CORRECT_ is now also used for a number of other behaviour quirks, where "POSIX and common sense disagree".

POSIX-ORIENTED OPERATING SYSTEMS

Depending upon the degree of compliance with the standards, one can classify operating systems as fully or partly POSIXcompatible. Certified products can be found at the IEEE's website.

POSIX-CERTIFIED

Some versions of the following operating systems have been certified to conform to one or more of the various POSIXstandards. This means that they passed the automated conformance tests.

* AIX * HP-UX * IRIX * EulerOS * OS X/macOS (since 10.5 Leopard ) * Solaris * Tru64 * UnixWare
UnixWare
* QNXNeutrino * Inspur K-UX * Integrity

MOSTLY POSIX-COMPLIANT

_ THIS SECTION NEEDS EXPANSION. You can help by adding to it . (January 2007)_

The following, while not officially certified as POSIXcompatible, comply in large part:

* Android (Available through Android NDK) * BeOS(and subsequently Haiku ) * Contiki * Darwin (core of OS X/macOS and iOS ) * FreeBSD
FreeBSD
* illumos * Linux
Linux
(most distributions — see Linux
Linux
Standard Base ) * LynxOS * MINIX(now MINIX3)S * MPE/iX * NetBSD
NetBSD
* Nucleus RTOS * NuttX * OpenBSD * OpenSolaris * PikeOS
PikeOS
RTOS for embedded systems with optional PSE51 and PSE52 partitions; see partition (mainframe) * Redox * RTEMS POSIXAPI support designed to IEEE Std. 1003.13-2003 PSE52 * Sanos * SkyOS * Syllable * VSTa * VxWorks( VxWorksis often used as a shell around non- POSIXKernels — i.e. TiMOS/SROS) * Xenix
Xenix

POSIXFor Microsoft
Microsoft
Windows

* Cygwinprovides a largely POSIX-compliant development and run-time environment for Microsoft Windows
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. * Microsoft POSIX subsystem, an optional Windows subsystem included in Windows NT-based operating systems up to Windows 2000. POSIX-1 as it stood in 1990 revision, without threads or sockets. * Interix, originally OpenNT by Softway Systems, Inc., is an upgrade and replacement for Microsoft POSIX subsystemthat was purchased by Microsoft
Microsoft
in 1999. It was initially marketed as a stand-alone add-on product and then later included it as a component in Windows Services for UNIX
Windows Services for UNIX
(SFU) and finally incorporated it as a component in Windows Server 2003 R2and later Windows OS releases under the name "Subsystem for UNIX-based Applications" (SUA); later made deprecated in 2012 (Windows 8) and dropped in 2013 (2012 R2, 8.1). It enables full POSIXcompliance for certain Microsoft
Microsoft
Windows products. * Windows Subsystem for Linux
Linux
is a compatibility layer for running Linux
Linux
binary executables natively on Windows 10 using an Ubuntu image, acting as an upgrade and replacement for Windows Services for UNIX. It was released in beta in April 2016. * UWINfrom AT"> * TRON project– alternative OS standards to POSIX * Common User Access– User interface standard * Interix– a full-featured POSIXand Unix
Unix
environment subsystem for Microsoft's Windows NT-based operating systems * C POSIX library * Real-time operating system * Portable character set

REFERENCES

* ^ "POSIX.1 FAQ". The Open Group. 5 October 2011. * ^ _A_ _B_ " POSIX1003.1 FAQ Version 1.12". 2 February 2006. Retrieved 16 July 2006. * ^ "POSIX". _Standards_. IEEE. * ^ "The origin of the name POSIX.". 2011. Retrieved 28 September 2013. * ^ PASC Status (including POSIX) (Report). IEEE Computer Society. 2003-12-04. Retrieved 2015-03-01. * ^ "Shell Command Language - The Open GroupBase Specifications Issue 7, 2013 Edition". * ^ "POSIX". The Open Group. * ^ "librt(3LIB)". _docs.oracle.com_. man pages section 3: Library Interfaces and Headers. Oracle Corporation. 1998-08-04. Retrieved 2016-02-18. librt, libposix4- POSIX.1b Realtime Extensions library librt is the preferred name for this l