Content

 

Introductory

The importance of the POSIX standard

POSIX (Portable Operating System Interface) is a collection of standards created to promote compatibility between operating systems. POSIX standards are crucial in the world of software development, especially for those working with UNIX-based systems such as Linux. These standards ensure that different operating systems handle file systems, character devices, and other basic system-level functions in a similar way.

The relationship between UNIX systems and POSIX

The POSIX standards specifically target the problems that have arisen from the widespread use of UNIX systems. In the 1980s, when UNIX systems became more and more popular, developers faced the problem that different versions of UNIX were not compatible with each other. Solving this was a big challenge in terms of software portability. The introduction of POSIX standards became a "common language" for UNIX systems, allowing developers to more easily adapt their applications to different UNIX-based systems.

 

In this review, we review the history and principles of the POSIX standards, as well as various aspects of the standard, such as the programming interface, file system and process management, network communication, and user and authorization management. In these sections, we review how these standards have shaped and are still shaping the development and interoperability of UNIX and UNIX-like systems.

 

 

History of the POSIX standard

Reasons for creating the standard

In the 1980s, during the spread of UNIX systems, different manufacturers developed their own versions. These systems were often incompatible with each other, making software portability significantly more difficult. The main reason for creating the standard was to provide a uniform basis for UNIX systems, thereby facilitating the work of software developers and easier interoperability between different systems.

The main milestones in the development of POSIX

The first version of the POSIX standard, IEEE 1003.1, was published in 1988. This standard defined basic interfaces such as file management, thread management, and process management. After that, many improvements and additions were released, covering more and more areas, including network services as well as graphical user interfaces.

In the 2000s, the POSIX standards received further updates to adapt them to the needs of modern computing. Updates included better multithreading support, introduction of safer programming techniques, and improvements to network communication.

POSIX standards are partially supported not only by UNIX-like systems, but also by other operating systems such as Windows and MacOS, which further increases their relevance and applicability on different platforms.

 

Principles of the POSIX standard

Main features and specifications

The POSIX standards contain a set of basic specifications that aim to unify operating systems and applications running on them. These include definitions of file system operation, process management, and threading mechanisms. POSIX specifications ensure that developers can use the same calls and interfaces on different systems, increasing code portability.

The standard also details the behavior of the shell and basic command-line tools, including text editors, file managers, and other basic system tools. It also defines the handling of character sets and localization (language and regional settings), which are important for software operating in a global market.

Compatibility with other systems

An essential element of the POSIX standards is the ability to promote compatibility between different operating systems. This allows developers to run the same code with little or no modification on various UNIX-like systems such as Linux, BSD, and Solaris. In addition, partial support for POSIX standards can be found in other operating systems, such as Microsoft Windows, which provide POSIX compatibility through various tools and subsystems (such as the Windows Subsystem for Linux).

This compatibility greatly contributes to the wide availability of software and interoperability between operating systems, promoting the efficient work of software developers and a wide selection of software for users.

 

 

Programming interface

POSIX API

The POSIX API (Application Programming Interface) is one of the most important parts of the POSIX standard, which defines the programming interfaces provided by operating systems. This includes file management, process and thread management, and timing and communication. The POSIX API allows developers to write applications that run on a wide range of UNIX-like systems without having to make significant changes to their code.

The POSIX API is based on the C programming language, which is widely used in low-level systems programming. The standard defines in detail the system calls, libraries, and other interfaces that developers can use to perform system-level operations.

Common POSIX calls and their usage

The POSIX API contains a number of basic system calls, some of the most commonly used are:

• File management: Az open (), read (), write (), and close () calls allow files to be opened, read, written, and closed. They form the basis of basic file management operations in any UNIX-like system.
• Process management: A fork () and exec () calls are used to create processes and start new programs. The wait() function allows parent processes to wait for child processes to complete.
• Fiber treatment: Functions of POSIX threads, or Pthreads, such as pthread_create() and pthread_join(), allow the development of multi-threaded applications that can efficiently use multi-core processors.
• Timing and Applications: Az alarm() and sleep () calls are used for timing and temporarily pausing processes, which can be important in certain types of applications, such as those that perform timed operations.

These calls and many others form the basis of the POSIX API, which enables developers to create efficient, portable, and stable applications on UNIX-like systems.

 

File system and processes

POSIX file system standards

The POSIX standards contain detailed specifications for file systems that govern the storage and handling of data in operating systems. The POSIX file system standards define the following basic concepts and operations:

• File and directory operations: Create, delete, rename, and manage file attributes, and create and navigate directories.
• Symbolic and hard links: POSIX standards support symbolic links (symlinks), which are references to a file or directory, and hard links, which point directly to blocks of data.
• File system permissions and properties: Manage file system permissions, including user and group permissions, and setting file and directory properties.

Process management based on POSIX

Process management is another key area of ​​the POSIX standards that allows operating systems to efficiently manage running applications and services. The basic process management concepts of POSIX are:

• Processes and Threads: Create, execute, and terminate processes and support multi-threaded programming.
• Signals: Signals sent by the system or by other processes that can be used by processes to respond to various events, such as an interruption or shutdown.
• Interprocess communication (IPC): Various methods, such as pipes, message queues, and shared memory, which enable data exchange and communication between processes.

These process management and file system standards ensure that UNIX-like systems handle basic system-level operations in a uniform and consistent manner, allowing for broad software portability and interoperability across platforms.

 

 

Network communication

POSIX standards in network communication

Network communication is a vital part of modern operating systems, and the POSIX standards provide uniform interfaces and protocols in this area as well. The POSIX standards for network communication allow developers to create network applications that are compatible with various UNIX-like systems.

• Socket programming: The definition of the POSIX standards includes the socket API, which is the basic mechanism for network communication based on TCP/IP protocols. THE socket(), bind(), listen(), accept(), connect(), send() and recv() functions enable the development of server and client applications.
• Network data transfer: POSIX standards define the methods of data transfer, including the format of data packets and the management of data streams. This allows developers to efficiently manage the transfer of data across networks.
• Network security and protocols: POSIX standards also take into account network security issues, ensuring the integrity and security of data when communicating over the network.

Common network operations and POSIX APIs

The POSIX standards provide a wide range of support for network operations, including:

• Create and manage connections: Sockets allow developers to establish connections between client and server applications, allowing data exchange and communication.
  Network streams: Data streams are handled through the POSIX APIs, which ensure the smooth flow of data across network connections.
• Network error management: Error handling during network communication is also part of the POSIX standards, ensuring the stability and reliability of network applications.

These network communication standards and APIs are fundamental to the development of network applications, enabling developers to create network functions in a consistent and efficient manner.

 

User and authorization management

User identification and authorizations

The POSIX standards also cover user identification and the management of authorization systems, which are fundamental to the security and access management of operating systems. These standards ensure that users and groups are managed in a uniform manner across different UNIX-like systems.

• User and group IDs: In POSIX systems, each user and group has a unique identifier (UID and GID) that defines the rights to the resources the system can access.
• File and directory permissions: File and directory permission management is part of the POSIX standards, allowing separate control of access rights for owner, group, and other users.
• Privilege levels: POSIX systems support different privilege levels, including normal user privileges and root privileges, which provide more extensive access to system resources.

Security features in POSIX

Security is an extremely important aspect of the POSIX standard. Safety features of the standard include:

• Restriction of rights: Systems allow for strict restrictions on privileges to prevent unauthorized access and abuse of system resources.
• Auditing and logging: System logging and auditing mechanisms ensure that system usage can be tracked, which is important for investigating security incidents and maintaining system integrity.

These user and privilege management standards ensure that UNIX-like systems can manage user access and resources in a secure and efficient manner.

 

 

Summary and vision

The current state of the POSIX standard

POSIX standards are now widely accepted and used among UNIX-like operating systems, ensuring application portability and cross-system compatibility. Standards are constantly evolving to meet modern computing needs and technological changes. Thanks to the POSIX standards, developers can create applications that can be easily adapted to different systems, increasing the availability and flexibility of software.

Expected developments and future directions

In the future, POSIX standards are expected to continue to evolve to address the ever-changing technology environment and the needs of the development community. Some possible directions in which the POSIX standards may evolve are:

• Cloud and remote support: As cloud-based services become more important, POSIX standards must ensure support for cloud-based infrastructures and remote computing environments.
• Security and privacy fixes: As security threats and data protection concerns increase, POSIX standards must pay close attention to these issues as well, ensuring the reliability and integrity of systems and applications.
• Environmental and energy efficiency aspects: Environmentally conscious technology and energy efficiency are increasingly emphasized in computing, which may influence the development of POSIX standards in the future.

Overall, POSIX standards continue to play a key role in the design and development of IT systems, ensuring portability, compatibility and flexibility in a changing technology environment.