Overview of the location of the Linux kernel in the entire operating system

The Linux kernel is not isolated. It must be studied in the entire system. Figure 1.1 shows the location of the Linux kernel in the entire operating system
:
User Process

System Call Interface




Hardware

Linux Kernel

Figure 1.1 Location of the Linux kernel in the entire operating system

As can be seen from Figure 1.1, the Linux operating system consists of four parts:
1. User Process & mdash; User application is a huge collection of software running at the highest level of the Linux operating system. When a user program runs on top of the operating system, it becomes a process in the operating system.
2. System Call Interface — In an application, a specific procedure in the operating system kernel can be called through a system call to implement a specific service. For example, if you schedule a system call to create a process in your program, the operating system kernel creates a new process for it.
The system call itself is also a process consisting of several instructions. But it is different from the general process. The main difference is that the system call is running in kernel mode (or system state), and the general process is running in user mode. In Linux, system calls are part of the kernel code.
3. Linux kernel — this is the focus of this book. The kernel is the soul of the operating system. It is responsible for managing files and memory on the disk, starting and running programs, receiving and sending data packets from the network, and so on. In short, the kernel is actually the interface between abstract resource operations and specific hardware operation details.
4. Hardware — This subsystem includes all possible physical devices required for Linux installation. For example, CPU, memory, hard drive, network hardware, and more.
The above division divides the entire Linux operating system into four levels. The user process is also included in the scope of the operating system because the operation of the user process is closely related to the operating system, and the system call interface can be said to be an extension of the operating system kernel, and the hardware is the material condition on which the operating system kernel depends. These four levels of dependencies are expressed as: the upper layer depends on the lower layer.