Linux Architecture

Linux-based OSes, unlike certain other operating systems, are constructed with a modular design that clearly separates the kernel from the user space. This design provides benefits in terms of both security and stability. Linux-based OSes consists of key components such as the Kernel, User Space, System Calls, Libraries (Optional), Desktop Environment (Optional), and System Utilities.

Key Concepts:

• Multi-user: One of Linux’s key strengths is its capability to accommodate numerous users at the same time. Every individual user possesses a specific account that grants different levels of access and permissions. There is an exclusive root user with administrative rights for making changes across the entire system. Other users have the ability to complete tasks within the permissions assigned to them. The su command permits authorized users to switch temporarily to the root account for administrative tasks.
• Multi-tasking: Linux is great at managing numerous programs (processes) simultaneously. It effectively distributes resources, guaranteeing each process gets the required CPU time and memory for seamless operation. This enables users to perform multiple tasks at the same time without experiencing major delays.

User Space vs. Kernel Space:

• Kernel Space: The heart of Linux, known as the kernel, is located in a secure memory region called kernel space. It manages hardware resources, oversees processes, and offers essential features such as memory management and security. Kernel space is heavily guarded because of its important function and is inaccessible to user applications without restriction.
• User Space: This is the location where user applications and processes are executed. Applications have a designated memory space and can only interact with system resources via regulated mechanisms known as system calls. This division ensures that the system is protected from potential crashes or malfunctions triggered by faulty applications. If a program faces an issue in user space, it generally won’t crash the whole system as opposed to a kernel panic.

System Calls and Libraries:

• System Calls: Utilized by applications to ask the kernel for particular services. These calls serve as a connection between user space and kernel space, enabling applications to reach hardware resources, file systems, and other functions that need kernel privileges. Linux offers a diverse range of system calls for different functions, such as handling files (open, read, write), managing processes, and communicating over networks.
• Libraries: Numerous apps make use of existing libraries with pre-written code functions. These libraries streamline the development process and offer standard features for various applications. Wrappers for system calls can be added to facilitate programmers’ interaction with the kernel.

The Benefits of This Structure:

The separation of user space and kernel space offers several advantages:

• Improved Stability: Mistakes made in user applications are unlikely to cause the entire system to crash, since they are isolated within their own environment.
• Enhanced Security: It is challenging for malicious apps to compromise the system because they are unable to access kernel resources directly.
• Modular Design: The modular structure makes it simpler to develop and maintain the kernel and user applications.

Conclusion

Pressing the power button on your computer initiates the bootloader, usually GRUB, loading the Linux kernel into RAM. It then identifies hardware, launches the init system (commonly systemd), and starts user applications, leading to a login screen. The kernel manages memory allocation, creates virtual memory, and establishes a virtual file system for file interaction. It communicates with peripheral devices through drivers but is protected by the CPU’s ring system, with the kernel at ring zero and regular users at ring three. System calls like writing files require transitioning to the kernel mode, often facilitated by wrappers in glibc, the GNU standard library for C, where the CPU temporarily elevates privileges to execute critical operations.

Once the task is completed, control returns to user mode to maintain system security and stability. To provide user-application separation, the kernel schedules processes, handles multitasking, and imposes access restrictions. This seamless synchronization of hardware and software permits the operating system to run efficiently, guaranteeing an ideal environment for user interactions and application execution.