The Single UNIX Specification (SUS) is the collective name of a family of standards for computer operating systems to qualify for the name "Unix". The SUS is developed and maintained by the Austin Group, based on earlier work by the IEEE and The Open Group.
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The SUS emerged from a mid-1980s project to standardize operating system interfaces for software designed for variants of the Unix operating system. The need for standardization arose because enterprises using computers wanted to be able to develop programs that could be used on the computer systems of different manufacturers without reimplementing the programs. Unix was selected as the basis for a standard system interface partly because it was manufacturer-neutral.
In 1988, these standards became IEEE 1003 (also registered as ISO/IEC 9945), or POSIX, which loosely stands for Portable Operating System Interface for uniX.
In the early 1990s, a separate effort known as the Common API Specification or Spec 1170 was initiated by several major vendors, who formed the COSE alliance in the wake of the Unix wars. This specification became more popular because it was available at no cost, whereas the IEEE charged a substantial fee for access to the POSIX specification.
In 1997, the Open Group released the Single UNIX Specification Version 2 [1].[1]
This specification consisted of:
and was at the core of the UNIX 98 brand [2].
Beginning in 1998, a joint working group known as the Austin Group began to develop the combined standard that would be known as the Single UNIX Specification Version 3 and as POSIX:2001 (formally: IEEE Std 1003.1-2001). It was released on January 30, 2002.[2]
This standard consisted of:
and is at the core of the UNIX 03 brand [3].
In 2004, a new edition of the POSIX:2001 standard was released, incorporating two technical corrigenda. It is called POSIX:2004 (formally: IEEE Std 1003.1-2004) [4].[3]
In December 2008, the Austin Group published a new major revision, known as POSIX:2008 (formally: IEEE Std 1003.1-2008) [5].[4][5] This is the core of the Single UNIX Specification, Version 4 [6]
This standard consists of:
SUSv3 totals some 3700 pages, which are thematically divided into four main parts:
The standard user command line and scripting interface is the POSIX shell, an extension of the Bourne Shell based on an early version of the Korn Shell. Other user-level programs, services and utilities include awk, echo, ed, vi, and hundreds of others. Required program-level services include basic I/O (file, terminal, and network) services. A test suite accompanies the standard. It is called PCTS or the POSIX Certification Test Suite.
Additionally, SUS includes CURSES (XCURSES) specification, which specifies 372 functions and 3 header files. All in all, SUSv3 specifies 1742 interfaces.
Note that a system need not include source code derived in any way from AT&T Unix to meet the specification. For instance, IBM OS/390, now z/OS, qualifies as a "Unix" despite having no code in common.
There are two official marks for conforming systems
Older UNIX standards (superseded)
AIX 5L V5.2 with some updates, AIX 5L V5.3 and AIX 6.1, are registered as UNIX 03 compliant. AIX 5L V5.2 is registered as UNIX 98 compliant.
HP-UX 11i V3 Release B.11.31 is registered as UNIX 03 compliant. Previous releases are registered as UNIX 95.
Mac OS X v10.5 "Leopard" and Mac OS X Server v10.5 "Leopard", released on October 26, 2007, are Open Brand UNIX 03 registered products when run on Intel processors,[7][8] as are Mac OS X v10.6 "Snow Leopard" and Mac OS X Server v10.6 "Snow Leopard".[9]
The last Reliant UNIX versions were registered as UNIX 95 compliant (XPG4 hard branding).
UnixWare 7.1.3 is registered as UNIX 95 compliant. SCO OpenServer 5 is registered as UNIX 93 compliant.
Solaris 10 is registered as UNIX 03 compliant on 32-bit and 64-bit x86 (X86-64) and SPARC systems. Solaris 8 and 9 are registered as UNIX 98 compliant on the same platforms, except that they do not include support for 64-bit x86 systems.
Solaris 2.5.1 was also registered as UNIX 95 compliant on the PReP PowerPC platform in 1996, but the product was withdrawn before more than a few dozen copies had been sold.[10]
Tru64 UNIX V5.1A and later are registered as UNIX 98 compliant.
IBM z/OS 1.2 and higher is registered as UNIX 95 compliant. z/OS 1.9, released on September 28, 2007, and subsequent releases "better align" with UNIX 03.[11]
Other operating systems registered as UNIX 95 or UNIX 93 compliant:
Vendors of Unix-like systems such as Linux and FreeBSD do not typically certify their distributions, as the cost of certification and the rapidly changing nature of such distributions make the process too expensive to sustain.[13]
No Linux distribution has been registered as SUS compliant.
The Linux Standard Base was formed in 2001 as an attempt to standardize the internal structures of Linux-based systems for increased compatibility. It is based on, and also extends in several areas, the POSIX specifications, the Single UNIX Specification and other open standards. It is de facto accepted and followed by many Linux distributions.
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