Posix
Posix
| Status | Published |
|---|---|
| Year started | 1988 |
| Latest version | IEEE Std 1003.1-20172017 |
| Organization | Austin Group(IEEE Computer Society,The Open Group,ISO/IEC JTC 1) |
| Related standards | ISO/IEC9945 |
| Domain | Application programming interfaces |
| Abbreviation | POSIX |
| Website |
The Portable Operating System Interface (POSIX)[1] is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines the application programming interface (API), along with command line shells and utility interfaces, for software compatibility with variants of Unix and other operating systems.[1][3]
| Status | Published |
|---|---|
| Year started | 1988 |
| Latest version | IEEE Std 1003.1-20172017 |
| Organization | Austin Group(IEEE Computer Society,The Open Group,ISO/IEC JTC 1) |
| Related standards | ISO/IEC9945 |
| Domain | Application programming interfaces |
| Abbreviation | POSIX |
| Website |
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 international standard name is ISO/IEC 9945.
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.).[5] The standardized user command line and scripting interface were based on the UNIX System V shell.[6] 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).
As of 2014, 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.[7]
The development of the POSIX standard takes place in the Austin Group (a joint working group linking the IEEE, The Open Group and the ISO/IEC JTC 1 organizations).
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) 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)[8]) 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
POSIX.1-2001 (or IEEE Std 1003.1-2001) equates to the Single UNIX Specification version 3. [9]
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)
POSIX.1-2008 (with two TCs)
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 and is, as of 22.7.2018, the current 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.[undefined] The variable name was later changed to POSIXLY_CORRECT.[15] This variable 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 POSIX compatible.
Certified products can be found at the IEEE's website.[16]
POSIX-certified
Some 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.[17]
Mostly POSIX-compliant
The following, while not officially certified as POSIX compatible, comply in large part:
Android (Available through Android NDK)
BeOS (and subsequently Haiku)
Contiki
Darwin (core of macOS and iOS)
DragonFly BSD
FreeBSD[29]
illumos
Linux (most distributions — see Linux Standard Base)
LynxOS
MINIX (now MINIX3)
MPE/iX[30]
NetBSD
Nucleus RTOS
NuttX
OpenBSD
OpenSolaris[31]
PikeOS RTOS for embedded systems with optional PSE51 and PSE52 partitions; see partition (mainframe)
Redox
RTEMS – POSIX API support designed to IEEE Std. 1003.13-2003 PSE52
SkyOS
Syllable
VSTa
VMware ESXi
VxWorks (VxWorks is often used as a shell around non-POSIX Kernels — i.e. TiMOS/SROS)
Xenix
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.
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 subsystem that was purchased by 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 (SFU) and finally incorporated it 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)[32] and dropped in 2013 (2012 R2, 8.1). It enables full POSIX compliance for certain Microsoft Windows products.
Windows Subsystem for Linux, also known as WSL, is a compatibility layer for running Linux binary executables natively on Windows 10 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.[33]
Windows C Runtime Library and Windows Sockets API implement commonly used POSIX API functions for file, time, environment, and socket access,[34] although the support remains largely incomplete and not fully interoperable with POSIX-compliant implementations.[35][36]
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 EMM386 /MULTI – a POSIX threads frontend API extension is available
Compliant via compatibility feature
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 noncompliant.
eCos – POSIX is part of standard distribution, and used by many applications. 'external links' section below has more information.
MorphOS (through the built-in ixemul library)
OpenVMS (through optional POSIX package)
Plan 9 from Bell Labs APE - ANSI/POSIX Environment[37]
RIOT (through optional POSIX module)
Symbian OS with PIPS (PIPS Is POSIX on Symbian)
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.[38] 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
UNIX System Services that runs on z/OS (certified as compliant)
See also
POSIX signal
POSIX Threads
POSIX sockets are basically Berkeley sockets
TRON project – alternative OS standards to POSIX
Common User Access – User interface standard
Interix – a full-featured POSIX and Unix environment subsystem for Microsoft's Windows NT-based operating systems
C POSIX library
Real-time operating system
Portable character set, set of 103 characters which should be supported in any POSIX-compliant character set locale