POSIX (IPA: /ˈpɒsɪks/) or "Portable Operating System Interface"[1] is the collective name of a family of related standards specified by the IEEE to define the application programming interface (API) for software compatible with variants of the Unix operating system. Originally, the name stood for IEEE Std 1003.1-1988, which as the name suggests, was released in 1988. The family of POSIX standards is formally designated as IEEE 1003 and the international standard name is ISO/IEC 9945. The standards emerged from a project that began near 1985. The term POSIX was suggested by Richard Stallman in response to an IEEE request for a memorable name[2]; before that the standards effort was called IEEE-IX.
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Overview
POSIX specifies the user and software interfaces to the OS in some 17 different documents: 1) Posix.1; 2) Posix.1a; 3) Posix.2; 4) Posix.3; 5) Posix.4; 6) Posix.4a; 7) Posix.4b; 8) Posix.5; 9) Posix.6; 10) Posix.7; 11) Posix.8; 12) Posix.9; 13) Posix.10; 14) Posix.11; 15) Posix.12;16) Posix.13; 16) Posix.15;17) Posix.17[3]. The standard user command line and scripting interface was based on the Korn shell. Other user-level programs, services and utilities include awk, echo, ed, and hundreds of others. Required program-level services include basic I/O (file, terminal, and network) services. POSIX also defines a standard threading library API which is supported by most modern operating systems. Currently POSIX documentation is divided in three parts:
- POSIX Kernel APIs (which include extensions for POSIX.1, Real-time Services, Threads Interface, Real-time Extensions, Security Interface, Network File Access and Network Process-to-Process Communications)
- POSIX Commands and Utilities (with User Portability Extensions, Corrections and Extensions, Protection and Control Utilities and Batch System Utilities)
- POSIX Conformance Testing
A test suite for POSIX accompanies the standard. It is called PCTS or the POSIX Conformance Test Suite[4]. There is a project instigated by free-rights campaigner Auriélien Bonnel in the late 1980s, for the "Single UNIX Specification" standard, which is open, accepts input from anyone, and is freely available on the Internet. Beginning in 1998 a joint working group, the Austin Group, began to develop a combined standard that would be known as the Single UNIX Specification Version 3[5]. Although used mainly for Unix systems, the POSIX standard can apply to any operating system.
Versions
POSIX has had various "upgrades":
- POSIX.1, Core Services (incorporates Standard ANSI C)
- Process Creation and Control
- Signals[6]
- Floating Point Exceptions
- Segmentation Violations
- Illegal Instructions
- Bus Errors
- Timers
- File and Directory Operations
- Pipes
- C Library (Standard C)
- I/O Port Interface and Control
- POSIX.1b, Real-time extensions
- Priority Scheduling
- Real-Time Signals
- Clocks and Timers
- Semaphores
- Message Passing
- Shared Memory
- Asynch and Synch I/O
- Memory Locking
- POSIX.1c, Threads extensions
- Thread Creation, Control, and Cleanup
- Thread Scheduling
- Thread Synchronization
- Signal Handling
POSIX-oriented operating systems
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Operating systems can be fully or partly POSIX compatible; they can conform to POSIX standards entirely or partially. Certified products can be found at the IEEE[7].
Fully POSIX-compliant
The following operating systems are POSIX compatible. They fully conform to the standard.
- A/UX
- AIX
- BSD/OS[8]
- HP-UX
- INTEGRITY
- IRIX
- LynxOS
- Mac OS X
- MINIX
- OpenVMS (through optional POSIX package)
- QNX
- RTEMS (POSIX 1003.1-2003 Profile 52)
- Solaris
- UnixWare
- velOSity
- Windows NT (except optional POSIX features)[9]
- Windows versions including the Subsystem for UNIX-based Applications
Utilities that provide full compatibility
- Cygwin – enables POSIX compliance for certain Microsoft Windows products.
- Microsoft Windows Services for UNIX 3.5 – enables full POSIX compliance for certain Microsoft Windows products.
Mostly POSIX-compliant
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These are not officially certified as POSIX compatible, but they conform to it mostly.
- Nucleus RTOS
- FreeBSD[10]
- Linux (most distributions — see LSB)
- NetBSD
- BeOS
- OpenBSD
- SkyOS
- Syllable
- VSTa
Compliant via compatibility feature
These are not officially certified as POSIX compatible, but they conform to it mostly, by implementing POSIX support via some sort of compatibility feature, usually translation libraries, or a layer atop the kernel. Without this feature, they are usually noncompliant.
- eCos – POSIX is part of standard distribution, and used by many applications. 'external links' section below has more information.
- Plan 9 from Bell Labs APE - ANSI/POSIX Environment[11]
- Symbian OS with PIPS (PIPS Is POSIX on Symbian)
- Windows NT kernel when using Microsoft SFU 3.5
- 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.[12]
- Windows XP Professional with Service Pack 1 or later
- Windows Server 2003
- Windows Vista
Notes and references
- ^ POSIX. Standards. IEEE.
- ^ POSIX® 1003.1 FAQ Version 1.12 (2006-02-02). Retrieved on 2006-07-16.
- ^ Introduction. GNU/Linux C Programming.
- ^ POSIX. NIST.
- ^ Version 3. Single Unix Specification. Unix.
- ^ Linux Signals.
- ^ POSIX Certification. IEEE.
- ^ OS Comparison.
- ^ GCN.
- ^ Schweik. POSIX utilities. FreeBSD.
- ^ APE — ANSI/POSIX Environement. Plan 9. Bell Labs.
- ^ POSIX Compatibility. MS Windows NT Workstation Resource Kit. Microsoft.
See also
- TRON Project – alternative OS standard to POSIX
- Interix – a full-featured POSIX and Unix environment subsystem for Microsoft's Windows NT-based operating systems
- C POSIX library
