Linux kernel is at the core of every Linux distribution and powers a majority of computer systems, from smartphones to servers. Understanding the architecture of the Linux kernel is essential for both developers and system administrators to effectively work with Linux.
In this blog post, we will take a deep dive into the Linux kernel architecture, starting from the boot process and going all the way to system calls.
Boot Process
The boot process of the Linux kernel is the crucial first step that sets the stage for the entire system to come alive. When the system is turned on, the BIOS or UEFI firmware loads the bootloader, which is usually GRUB or LILO. The bootloader then loads the Linux kernel into memory and passes control to it.
The kernel initializes the hardware, such as the CPU, memory, and storage devices, and sets up the initial execution environment. It then proceeds to mount the root filesystem and begins executing the init process, which is the first user-space process on the system.
Kernel Space and User Space
The Linux kernel employs a concept called "kernel space" and "user space" to provide separation between the kernel and user applications. The kernel space contains the kernel code and data structures, while the user space contains the user applications and libraries.
User applications can only interact with the kernel through a limited set of interfaces known as "system calls". These system calls allow the user applications to request services from the kernel, such as creating a new process or accessing hardware devices.
Kernel Modules
Linux kernel architecture supports the concept of loadable kernel modules, which are pieces of code that can be dynamically loaded and unloaded into the running kernel without rebooting the system. Modules enhance the flexibility and maintainability of the kernel by allowing new functionalities to be added or existing ones to be extended without modifying the base kernel.
Process Management
The Linux kernel employs a process management mechanism to handle the creation, execution, and termination of processes. Each process is represented by a task_struct data structure, which contains information about the process, such as its state, registers, and memory management.
The kernel scheduler is responsible for determining which process to execute on each CPU core. It uses various scheduling algorithms, such as the Completely Fair Scheduler (CFS), to allocate CPU time fairly among processes and prioritize them based on their priority or importance.
Memory Management
Memory management is a critical aspect of the Linux kernel architecture. The kernel is responsible for managing both physical and virtual memory. It assigns and deallocates memory to processes, manages the virtual memory mapping, and handles memory swapping to disk when the system is under memory pressure.
The Linux kernel uses a combination of paging and segmentation techniques to manage virtual memory. It implements the concept of a page table, which maps the virtual memory addresses to physical memory pages.
System Calls
System calls are the primary interface between user applications and the Linux kernel. They allow user applications to request privileged operations or access kernel services. Common system calls include file I/O, process management, networking, and inter-process communication.
When a user application makes a system call, it triggers a transition from user space to kernel space. The kernel verifies the requested operation, performs the necessary actions, and returns the result to the user application.
Conclusion
Understanding the Linux kernel architecture is essential for working with Linux systems effectively. From the boot process to system calls, the kernel plays a fundamental role in managing hardware resources, processes, and memory. By gaining insights into the Linux kernel architecture, developers and system administrators can optimize their code and efficiently troubleshoot system issues.
本文来自极简博客，作者：微笑绽放，转载请注明原文链接：Exploring Linux Kernel Architecture: From Boot to System Calls
