The Single UNIX® Specification, Version 3 and UNIX 03

A Technical White Paper from the Open Group.

Version 1.01 Last update April 2004.


Developed through the The Open Group consensus process the Single UNIX Specification Version 3 and the UNIX 03 Product Standards enhance the latest generation of UNIX systems, and reinforce the UNIX trademark as the industry recognized mark for the leading open operating environment. The specification brings all the benefits of a single standard operating system, namely application and information portability, scalability, flexibility and freedom of choice for customers. Continuing its commitment to Open Systems and open availability to its specifications, The Open Group is pleased to announce availability of the Single UNIX Specification, Version 3 on the World Wide Web at URL

1.1 Introduction - The Common Base Specifications

Version 3 of the Single UNIX Specification is built on the common foundation of the Austin Group specifications (see figure below) , which are simultaneously an IEEE Standard, an Open Group Technical Standard and an ISO/IEC International Standard. This Base document set is the common update to IEEE Std 1003.1,1996 Edition, IEEE Std 1003.2, 1992 Edition, their ISO/IEC counterparts and the previous version of the Single UNIX Specification. The common base specifications are widely supported by the industry, and also referenced by other specifications efforts such as the ELC and LSB specifications.

The complete Single UNIX Specification adds X/Open Curses Issue 4 Version 2 to the Base document set .

1.2 Benefits

Benefits for Application Developers

Benefits for Users

1.3 Changes to the Single UNIX Specification

The Single UNIX Specification Version 3 incorporates the following changes:

The additions due to IEEE P1003.1a draft standard and IEEE Std 1003.1g-2000 have been added to the mandatory requirements for the Single UNIX Specification, Version 3. The additions from IEEE Std 1003.1d-1999, IEEE Std 1003.1j-2000, and IEEE Std 1003.1q-2000 have in general been added as options. The reader-writer locks from IEEE Std 1003.1j-2000 duplicate the reader-writer locks already contained in the Single UNIX Specification, Version 2 and are still mandatory.

The 5.2 issue of the Networking Services specification superseded the version included in the Single UNIX Specification, Version 2. The main change was the addition of IPv6 functionality.

This is the latest version of the C programming language standard and is a change from the Single UNIX Specification, Version 2.

1.4 Interface Counts

As a result of the addition of new materials into the specification the interface count has risen. The Single UNIX Specification Version 3 now has over 1700 programming interfaces, and compares with other specifications as shown in the diagram below:

2.1 What is UNIX 03 ?

UNIX 03 is the mark for systems that a vendor guarantees as conforming to Version 3 of the Single UNIX Specification.

UNIX 03 is

If a product is registered as conformant to UNIX 03 the vendor warrants and represents that it:

UNIX 03 is organized as a series of product standards addressing different market needs. The first two of these are as follows (note that others may follow subsequently)

The following diagram shows the internet services included in the UNIX 03 Server product standard:

3.1 More Information

More information on the Single UNIX Specification, Version 3 can be obtained from the following sources:

Copyright The Open Group, © 2004

UNIX is a registered trademark of The Open Group