Otas is a RHEL Sysadmin at Lockheed Martin. She has been assigned to teach an incoming class of 50 interns about the history of GNU/Linux and Unix. Tomorrow, she will be giving a lecture on POSIX. Please describe the POSIX family of standards in great detail to give Otas something to read to prepare for her lecture.
POSIX (Portable Operating System Interface) is a family of standards that define a set of APIs (Application Programming Interfaces) and other specifications for ensuring compatibility between operating systems and applications. It was developed by the IEEE (Institute of Electrical and Electronics Engineers) in collaboration with the ISO (International Organization for Standardization) and the IEC (International Electrotechnical Commission).
The POSIX standards are primarily focused on providing a common interface for Unix-like operating systems, ensuring that software written for one POSIX-compliant system can be easily ported to another without significant modifications. The standards aim to promote interoperability, portability, and compatibility across various Unix-like systems, including Linux, BSD, and other derivatives.
The POSIX family of standards consists of several individual specifications, each addressing different aspects of the operating system and software development. Here are some of the key POSIX standards:
POSIX.1: This is the core standard of the POSIX family and defines the fundamental APIs for system services and utilities. It covers basic functionality such as process management, file management, input/output operations, signals, environment variables, and error handling.
POSIX.1b (Real-time Extensions): This standard extends the core POSIX.1 specification to include real-time features, such as real-time scheduling, synchronization, and inter-process communication mechanisms.
POSIX.1c (Threads Extensions): This standard adds support for thread management, allowing applications to create and manage multiple threads of execution within a process. It includes functions for thread creation, synchronization, and mutual exclusion.
POSIX.1d (Real-time Threads Extensions): This standard combines the features of POSIX.1b and POSIX.1c, providing real-time extensions for both processes and threads.
POSIX.2 (Shell and Utilities): This standard defines the command interpreter (shell) and a set of utility programs commonly found in Unix-like systems. It specifies the command syntax, environment variables, and utilities like file manipulation, text processing, and shell scripting.
POSIX.4 (Real-time and Threads): This standard consolidates the real-time and threads extensions from POSIX.1b, POSIX.1c, and POSIX.1d, providing a unified specification for real-time and threaded programming.
POSIX.7 (System Interfaces): This standard extends the core POSIX.1 specification by adding additional system interfaces, including features like shared memory, semaphores, message queues, timers, and more.
In addition to these core standards, there are several other POSIX-related specifications, such as POSIX.1e (File System Extended Attributes), POSIX.1f (Real-time File System), and POSIX.1g (Network File System). These extensions provide further enhancements to specific areas of the operating system.
It's important to note that while POSIX standards define a common set of interfaces, they do not specify the underlying implementation details or architecture of an operating system. Therefore, POSIX-compliant systems can have different internal designs and performance characteristics, as long as they provide the required APIs and functionality defined by the POSIX standards.
By adhering to the POSIX standards, system developers and application programmers can ensure their software is portable and can run on a wide range of Unix-like systems, promoting interoperability and reducing the effort required for software migration and compatibility.