Open System Services Programmer's Guide

The OSS API
An application program interface (API) is a set of functions or procedure calls that permits user
programs to communicate with the operating system. The OSS API coexists on NonStop systems
with the traditional Guardian interfaces, as shown in Figure 1.
Figure 1 The Operating Environment for NonStop Systems
An application program can be compiled to run in either the OSS or Guardian environment and
can use services from each environment, including the API, tools, and utilities.
Standards Conformance
The OSS API conforms to the POSIX.1 and POSIX.2 standards, and partially conforms to the XPG4
specifications. These standards and specifications are described in the following documents:
• Information Technology – Portable Operating System Interface (POSIX) – Part 1: System
Application Program Interface (API) [C Language], ISO/IEC 9945-1 (IEEE Std 1003.1,
SH13680), First Edition 1990.
• Information Technology – Portable Operating System Interface (POSIX) – Part 2: Shell and
Utilities, ISO/IEC 9945-2 (IEEE Std 1003.2a), First edition 1992.
• X/Open CAE Specifications – System Interfaces and Headers, Issue 4.
• X/Open CAE Specifications – System Interfaces and Headers, Issue 4, Version 2.
Conformance to POSIX.1
You might need to write applications that strictly conform to a certain standard or specification. A
strictly-conforming POSIX.1 application cannot use any of the following:
• Any function unique to a NonStop system, such as tdm_fork(), that is an extension to the
standard.
• The Guardian environment. This is not discussed by the standard.
• A Guardian object. This is not discussed by the standard.
• A remotely mounted fileset. This is not discussed by the standard.
• A symbolic link. This is not discussed by the current version of the standard.
• A POSIX.2 function, such as those provided in the regex.h and glob.h header files.
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