1. Preface — RTEMS POSIX API Guide 5.4-rc2 (21st August 2026) documentation

# 1. Preface

This is the User’s Guide for the POSIX API support provided in RTEMS.

The functionality described in this document is based on the following standards:

- POSIX 1003.1b-1993.

- POSIX 1003.1h/D3.

- Open Group Single UNIX Specification.

Much of the POSIX API standard is actually implemented in the Cygnus Newlib ANSI C Library. Please refer to documentation on Newlib for more information on the functionality it supplies.

This manual is still under construction and improvements are welcomed from users.

## 1.1. Acknowledgements

The RTEMS Project has been granted permission from The Open Group IEEE to excerpt and use portions of the POSIX standards documents in the RTEMS POSIX API User’s Guide and RTEMS Shell User’s Guide. We have to include a specific acknowledgement paragraph in these documents (e.g. preface or copyright page) and another slightly different paragraph for each manual page that excerpts and uses text from the standards.

This file should help ensure that the paragraphs are consistent and not duplicated

> The Institute of Electrical and Electronics Engineers, Inc and The Open Group, have given us permission to reprint portions of their documentation. Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (c) 2001-2004 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html. This notice shall appear on any product containing this material.