LWM-Linux/01 - Introduction to Linux/Linux Operating System Structure.md

Linux Operating System Structure

1. Kernel:

• The kernel is the core of the Linux operating system.
• It is responsible for managing the system's hardware resources, such as the CPU, memory, and I/O devices.
• The kernel provides an abstraction layer between the hardware and the software, allowing applications to interact with the hardware without needing to know the specific details of the underlying hardware.
• The kernel is responsible for tasks such as process management, memory management, file management, and device management.
• The Linux kernel is typically monolithic, meaning that all the kernel functions are in a single, large executable.
• The kernel can be customized and configured to meet the specific needs of the system.

2. User Space:

• The user space is the area of the operating system where user-level applications and processes run.
• User-level applications, such as web browsers, email clients, and text editors, are not part of the kernel and run in the user space.
• The user space is where most of the day-to-day activities of the system take place.
• User-level applications interact with the kernel through system calls, which are a set of interfaces provided by the kernel.

3. File System:

• The file system is the way in which files and directories are organized and stored on the storage devices.
• Linux supports various file systems, such as ext4, XFS, Btrfs, and more.
• The file system is responsible for managing the storage, retrieval, and organization of files and directories.
• The file system provides a hierarchical structure, where files and directories are organized in a tree-like structure, with the root directory at the top.
• The file system also manages permissions and access control to files and directories.

4. Boot Process:

• The boot process is the sequence of events that occurs when the system is powered on or restarted.
• The boot process starts with the BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface), which performs hardware checks and loads the boot loader.
• The boot loader, such as GRUB (Grand Unified Bootloader) or systemd-boot, is responsible for loading the kernel and the initial ramdisk (initrd) into memory.
• The kernel then takes over and initializes the system, loading various kernel modules and starting the init system (such as systemd or SysVinit).
• The init system is responsible for starting and managing the various services and processes that make up the operating system.

5. Process Management:

• The process management subsystem is responsible for managing the execution of processes and threads.
• Processes are instances of running programs, and threads are lightweight processes that share the same memory space.
• The kernel is responsible for creating, scheduling, and terminating processes and threads.
• The process management subsystem also includes features like inter-process communication (IPC), which allows processes to exchange data and synchronize their execution.

6. Memory Management:

• The memory management subsystem is responsible for managing the system's physical and virtual memory.
• The kernel provides a virtual memory system, which allows applications to use more memory than is physically available on the system.
• The memory management subsystem is responsible for allocating and freeing memory, as well as implementing techniques like paging and swapping to manage the virtual memory system.

7. Device Management:

• The device management subsystem is responsible for managing the various hardware devices connected to the system.
• The kernel provides a uniform interface for interacting with devices, abstracting away the details of the underlying hardware.
• The device management subsystem includes drivers for different types of devices, such as storage devices, network devices, and input/output devices.
• The device management subsystem also includes a plug-and-play system, which allows devices to be automatically detected and configured when they are connected to the system.

8. Network Stack:

• The network stack is the set of protocols and services that enable network communication in the Linux operating system.
• The network stack includes protocols like TCP/IP, UDP, and ICMP, as well as higher-level protocols like HTTP, FTP, and SSH.
• The network stack is responsible for sending and receiving network packets, as well as managing network interfaces and routing.
• The network stack also includes features like firewalling, network address translation (NAT), and virtual private networks (VPNs).