By Wikipedia, the free encyclopedia
Originally, the name "POSIX" referred to IEEE Std 1003.1-1988, released, as the name suggests, in 1988. The family of POSIX standards is formally designated as IEEE 1003 and the international standard name is ISO/IEC 9945.
The standards, formerly known as IEEE-IX, emerged from a project that began circa 1985. Richard Stallman suggested the name POSIX in response to an IEEE request for a memorable name.
The POSIX specifications for Unix-like operating system environments originally consisted of a single document for the core programming interface, but eventually grew to 17 separate documents. The standardized user command line and scripting interface were based on the Korn 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) services. POSIX also defines a standard threading library API which is supported by most modern operating systems. Nowadays, 10 out of these 17 parts are combined into a single standard, IEEE Std 1003.1-2008, also known as POSIX:2008.
As of 2009, POSIX documentation is divided in two parts:
A test suite for POSIX accompanies the standard: PCTS or the POSIX Conformance Test Suite.
The development of the POSIX standard takes place in the Austin Group, a joint working group linking the Open Group and the ISO organization.
Parts before 1997
Before 1997, POSIX comprised several standards:
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:2001 or IEEE Std 1003.1-2001 equates to the Single UNIX Specification version 3
This standard consisted of:
POSIX:2004 or IEEE Std 1003.1-2004 involved a minor update of POSIX:2001. It incorporated two technical corrigenda. Its contents are available on the web.
As of 2009 POSIX:2008 or IEEE Std 1003.1-2008 represents the current version. A free online copy is available.
This standard consists of:
512- vs 1024-byte blocks
POSIX mandates 512-byte block sizes for the df and du utilities, reflecting the default 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 environmental variable POSIXLY_CORRECT was introduced to force the standards-compliant behaviour. The variable POSIX_ME_HARDER was also discussed and was implemented in a few packages before being obsoleted by POSIXLY_CORRECT.
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.
The following operating systems conform (i.e., are 100% compliant) to one or more of the various POSIX standards.
The following, while not officially certified as POSIX compatible, conform in large part:
POSIX for Windows
POSIX for OS/2
Mostly POSIX compliant environments for OS/2:
POSIX for DOS
Partially POSIX compliant environments for DOS include:
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.
Published - December 2011
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