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1. Linux-Programming-introduction

1. What is System Programming?​

  • Linux system programming refers to writing programs that run on the Linux operating system, which can directly interact with the Linux kernel and utilize various system calls and library functions provided by the operating system to achieve various functionalities. Linux system programming typically requires a deep understanding of the internal mechanisms and implementation principles of the Linux operating system, as it involves utilizing low-level mechanisms such as system calls, threads, processes, signals, and file I/O to develop efficient, stable, and reliable programs.
  • In Linux system programming, developers can use various programming languages such as C, C++, Python, etc., and development tools like editors, debuggers, compilers, etc., to write programs. Linux system programming can be applied in various domains, such as network programming, system administration, embedded systems, security, and more.

2. Linux System Layered Architecture​

  • User Space: The user space is the highest layer of the Linux system, encompassing all user processes and applications. In this layer, users can run various software, such as text editors, browsers, image processing tools, etc. It also includes the file systems accessible to users and various system services and utilities.

  • System Call Interface: The system call interface serves as the layer between the Linux kernel and the user space. In this layer, applications use system calls to send requests to the kernel to obtain system resources or perform specific operations. The system call interface provides a set of standardized system calls, such as reading and writing files, creating and managing processes, and more.

  • Kernel Space: The kernel space is the intermediate layer of the Linux system, consisting of kernel code and data structures. In this layer, the kernel provides various services and functionalities, such as process management, file system management, network management, device drivers, etc. It also includes various kernel subsystems and modules, such as memory management, schedulers, security modules, etc.

  • Hardware Layer: The hardware layer is the lowest layer of the Linux system, comprising various physical devices, such as CPU, memory, disks, network interface cards, etc. In this layer, the kernel interacts with hardware devices using device drivers to control and manage them.

3. Introduction to POSIX Standards​

POSIX (Portable Operating System Interface) is a series of standards jointly developed by IEEE and Open Group. The standards aim to define a set of operating system interfaces, enabling portability between different operating systems. The POSIX standards mainly include the following aspects:

  • System Calls: Defining a set of standardized system call interfaces, including file operations, process management, signal handling, etc
  • Library Functions: Defining a set of standardized library function interfaces, including mathematical functions, string operations, time functions, etc
  • Command-Line Interface: Defining a set of standardized command-line interfaces, including command-line options, environment variables, standard input/output, etc
  • Thread Interface: Defining a set of standardized thread interfaces, including thread creation, synchronization, destruction, etc

POSIX standards are widely applied in Unix and Unix-like operating systems, such as Linux, macOS, etc. By utilizing the POSIX standards, developers can write programs that are independent of specific operating systems, thereby enhancing program portability and reusability.