The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

POSIX.1-2008 is simultaneously IEEE Std 1003.1-2008 and The Open Group Technical Standard Base Specifications, Issue 7. This 2016 Edition includes IEEE Std 1003.1-2008/Cor 1-2013 and IEEE Std 1003.1-2008/Cor 2-2016 incorporated into IEEE Std 1003.1-2008 (the base document). The Technical Corrigendum addresses problems discovered since the approval of IEEE Std 1003.1-2008


This introduction is not part of IEEE Std 1003.1, 2016 Edition, Standard for Information Technology – Portable Operating System Interface (POSIX).

This standard was developed, and is maintained, by a joint working group of members of the IEEE Portable Applications Standards Committee, members of The Open Group, and members of ISO/IEC Joint Technical Committee 1. This joint working group is known as the Austin Group.B

The Austin Group arose out of discussions amongst the parties which started in early 1998, leading to an initial meeting and formation of the group in September 1998. The purpose of the Austin Group is to develop and maintain the core open systems interfaces that are the POSIX® 1003.1 (and former 1003.2) standards, ISO/IEC 9945, and the core of the Single UNIX Specification.

The approach to specification development has been one of “write once, adopt everywhere”, with the deliverables being a set of specifications that carry the IEEE POSIX designation, The Open Group's Technical Standard designation, and an ISO/IEC designation.

This unique development has combined both the industry-led efforts and the formal standardization activities into a single initiative, and included a wide spectrum of participants. The Austin Group continues as the maintenance body for this document.

Anyone wishing to participate in the Austin Group should contact the chair with their request. There are no fees for participation or membership. You may participate as an observer or as a contributor. You do not have to attend face-to-face meetings to participate; electronic participation is most welcome. For more information on the Austin Group and how to participate, see


The developers of POSIX.1-2008 represent a cross-section of hardware manufacturers, vendors of operating systems and other software development tools, software designers, consultants, academics, authors, applications programmers, and others.

Conceptually, POSIX.1-2008 describes a set of fundamental services needed for the efficient construction of application programs. Access to these services has been provided by defining an interface, using the C programming language, a command interpreter, and common utility programs that establish standard semantics and syntax. Since this interface enables application developers to write portable applications – it was developed with that goal in mind – it has been designated POSIXC, an acronym for Portable Operating System Interface.

Although originated to refer to the original IEEE Std 1003.1-1988, the name POSIX more correctly refers to a family of related standards: IEEE Std 1003.n and the parts of ISO/IEC 9945. In earlier editions of the IEEE standard, the term POSIX was used as a synonym for IEEE Std 1003.1-1988. A preferred term, POSIX.1, emerged. This maintained the advantages of readability of the symbol “POSIX” without being ambiguous with the POSIX family of standards.


The intended audience for POSIX.1-2008 is all persons concerned with an industry-wide standard operating system based on the UNIX system. This includes at least four groups of people:


Several principles guided the development of POSIX.1-2008:

No direct references to this goal appear in POSIX.1-2008, but some results of it are mentioned in the Rationale (Informative) volume.

The adoption of the 1988 and 1990 IEEE system interface standards, the 1992 IEEE shell and utilities standard, the various Open Group (formerly X/Open) specifications, and IEEE Std 1003.1-2001 and its technical corrigenda have consolidated this consensus, and this version reflects the significantly increased level of consensus arrived at since the original versions. The authors of the original versions tried, as much as possible, to follow the principles below when creating new specifications:

POSIX.1-2008 is specifically not a codification of a particular vendor's product.

It should be noted that implementations will have different kinds of extensions. Some will reflect “historical usage” and will be preserved for execution of pre-existing applications. These functions should be considered “obsolescent” and the standard functions used for new applications. Some extensions will represent functions beyond the scope of POSIX.1-2008. These need to be used with careful management to be able to adapt to future extensions of POSIX.1-2008 and/or port to implementations that provide these services in a different manner.


POSIX.1-2008 defines the Portable Operating System Interface (POSIX) requirements and consists of the following topics arranged as a series of volumes within the standard:

Base Definitions

The Base Definitions volume provides common definitions for this standard, therefore readers should be familiar with it before using the other volumes.

This volume is structured as follows:

Comprehensive references are available in the index.

System Interfaces

The System Interfaces volume describes the interfaces offered to application programs by POSIX-conformant systems. Readers are expected to be experienced C language programmers, and to be familiar with the Base Definitions volume.

This volume is structured as follows:

Comprehensive references are available in the index.

Shell and Utilities

The Shell and Utilities volume describes the commands and utilities offered to application programs on POSIX-conformant systems. Readers are expected to be familiar with the Base Definitions volume.

This volume is structured as follows:

Comprehensive references are available in the index.

Rationale (Informative)

The Rationale volume is published to assist in the process of review. It contains historical information concerning the contents of this standard and why features were included or discarded by the standard developers. It also contains notes of interest to application programmers on recommended programming practices, emphasizing the consequences of some aspects of POSIX.1-2008 that may not be immediately apparent.

This volume is organized in parallel to the normative volumes of this standard, with a separate part for each of the three normative volumes.

Within this volume, the following terms are used:

B The Austin Group is named after the location of the inaugural meeting held at the IBM facility in Austin, Texas in September 1998.

C The Name POSIX was suggested by Richard Stallman. It is expected to be pronounced pahz-icks, as in positive, not poh-six, or other variations. The pronunciation has been published in an attempt to promulgate a standardized way of referring to a standard operating system interface.

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