POSIX
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POSIX 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[1]; before that the standards effort was called IEEE-IX.
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[edit] Overview
POSIX specifies the user and software interfaces to the OS in some 15 different documents. 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[2].
Since the IEEE charges very high rates for POSIX documentation and does not allow on-line publication of the standards, there has been a tendency toward 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[3].
Although used mainly for Unix systems, the POSIX standard can apply to any operating system.
[edit] Versions
POSIX has had various "upgrades":
- POSIX.1, Core Services (incorporates Standard ANSI C)
- Process Creation and Control
- Signals
- 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
[edit] POSIX-oriented operating systems
Operating systems can be fully or partly POSIX compatible; they can conform to POSIX standards entirely or partially. Certified products can be found at IEEE's POSIX Certification website.
[edit] Fully POSIX-compliant
These are POSIX compatible, they conform to it fully.
- A/UX
- BlagOS
- BSD/OS [4]
- Cygwin - enables POSIX compliance for certain Microsoft Windows products.
- AIX
- HP-UX
- velOSity
- INTEGRITY
- Irix
- LynxOS
- Mac OS X
- Microsoft Windows Services for UNIX 3.5 - enables POSIX compliance for certain Microsoft Windows products.
- MINIX
- OpenVMS
- penOS
- QNX
- RTEMS (POSIX 1003.1-2003 Profile 52)
- Solaris
- UnixWare
- VxWorks
- NT kernel (used in Windows NT, 2000, 2003; XP, Vista)
- Windows NT (except optional POSIX features) [5]
- Windows 2000 Server or Professional with Service Pack 3 or later (When using Microsoft SFU 3.5). To be POSIX compliant, one must activate optional features of Windows NT and Windows Server. [6]
- Windows XP Professional with Service Pack 1 or later (When using Microsoft SFU 3.5)
- Windows Server 2003 (When using Microsoft Windows Services for UNIX 3.5)
- Windows Vista (the Enterprise and Ultimate editions include a Microsoft Windows Services for UNIX subsystem for UNIX programs)
[edit] Mostly POSIX-compliant
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These are not officially certified as POSIX compatible, but they conform to it mostly.
[edit] 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 [8]
- Symbian OS with PIPS (PIPS Is POSIX on Symbian)
[edit] Notes and references
[edit] 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
