The standard specifies programming interfaces for the C language, a command-line shell, and user commands.
Very few BSD and Linux-based operating systems are submitted for compliance with the Single UNIX Specification, although system developers generally aim for compliance with POSIX standards, which form the core of the Single UNIX Specification.
[6] In 1988, standardization efforts resulted in IEEE 1003 (also registered as ISO/IEC 9945), or POSIX.1-1988, which loosely stands for Portable Operating System Interface.
XPG4 Base included the following documents: In the early 1990s, a separate effort known as the Common API Specification or Spec 1170 was initiated by several major vendors,[9] who formed the COSE alliance in the wake of the Unix wars.
[10] In October 1993, a planned transfer of UNIX trademark from Novell to X/Open was announced;[11] it was finalized in 2nd quarter of 1994.
[9] The SUS was made up of documents that were part of the X/Open Common Applications Environment (CAE):[9] This was a repackaging of the X/Open Portability Guide (XPG), Issue 4, Version 2.
Sources differ on whether X/Open Curses, Issue 4, Version 2 was part of this SUS;[9][17] its copyright date is given as 1996.
In December 2008, the Austin Group published a new major revision of SUS and POSIX.
Other user-level programs, services and utilities include awk, echo, ed, vi, and hundreds of others.
Additionally, SUS includes CURSES (XCURSES) specification, which specifies 372 functions and 3 header files.
Note that a system need not include source code derived in any way from AT&T Unix to meet the specification.
[52] There are five official marks for conforming systems:[53][54] AIX version 7, at either 7.1 TL5 (or later) or 7.2 TL2 (or later) are registered as UNIX 03 compliant.
[72] Stratus Technologies DNCP Series servers running FTX Release 3 were registered as UNIX 93 compliant.
[63] Solaris 2.5.1 was also registered as UNIX 95 compliant on the PReP PowerPC platform in 1996, but the product was withdrawn before more than a few dozen copies had been sold.
[82] Other operating systems previously registered as UNIX 95 or UNIX 93 compliant: Developers and vendors of Unix-like operating systems such as Linux, FreeBSD, and MINIX typically do not certify their distributions and do not install full POSIX utilities by default.
[83] Sometimes, SUS compliance can be improved by installing additional packages, but very few Linux systems can be configured to be completely conformant.
[86] Darwin, the open source subset of macOS, has behavior that can be set to comply with UNIX 03.
[citation needed] FreeBSD previously had a "C99 and POSIX Conformance Project" which aimed for compliance with a subset of the Single UNIX Specification, and documentation where there were differences.
[93] OpenBSD man pages sometimes indicate deviations from POSIX and thus SUS in their STANDARDS sections.