Single UNIX Specification

The Single UNIX Specification (SUS) is a standard for computer operating systems,^[1][2] compliance with which is required to qualify for using the "UNIX" trademark. The standard specifies programming interfaces for the C language, a command-line shell, and user commands. The core specifications of the SUS known as Base Specifications are developed and maintained by the Austin Group, which is a joint working group of IEEE, ISO/IEC JTC 1/SC 22/WG 15 and The Open Group. If an operating system is submitted to The Open Group for certification, and passes conformance tests, then it is deemed to be compliant with a UNIX standard such as UNIX 98 or UNIX 03.

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.

The latest SUS consists of two parts: the base specifications technically identical to POSIX, and X/Open Curses specification.^[3]

Some parts of the SUS are optional.