Mohammad Abdullah Ansari’s Post

Linux Boot Process Explained Almost every software engineer has used Linux before, but only a handful know how its Boot Process works :) Let's dive in. The diagram below shows the steps. Step 1 - When we turn on the power, BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface) firmware is loaded from non-volatile memory, and executes POST (Power On Self Test). Step 2 - BIOS/UEFI detects the devices connected to the system, including CPU, RAM, and storage. Step 3 - Choose a booting device to boot the OS from. This can be the hard drive, the network server, or CD ROM. Step 4 - BIOS/UEFI runs the boot loader (GRUB), which provides a menu to choose the OS or the kernel functions. Step 5 - After the kernel is ready, we now switch to the user space. The kernel starts up systemd as the first user-space process, which manages the processes and services, probes all remaining hardware, mounts filesystems, and runs a desktop environment. Step 6 - systemd activates the default. target unit by default when the system boots. Other analysis units are executed as well. Step 7 - The system runs a set of startup scripts and configure the environment. Step 8 - The users are presented with a login window. The system is now ready.

I have recently started studying Embedded Linux using a SBC based on 𝐀𝐌335𝐱 processor and got to know few very interesting things related to 𝐁𝐨𝐨𝐭 𝐒𝐞𝐪𝐮𝐞𝐧𝐜𝐞 that I thought to share. 1. 𝐑𝐎𝐌 𝐁𝐨𝐨𝐭𝐥𝐨𝐚𝐝𝐞𝐫 (Read-Only Memory Bootloader): A ROM (Read-Only Memory) Bootloader is a small program stored in non-volatile memory (ROM) that initiates the boot process of a computing device. It resides in a chip on the device's motherboard and is typically provided by the hardware manufacturer. Its primary function is to initialize essential hardware components such as CPU, RAM, and peripherals to prepare the system for booting. Once initialized, the ROM Bootloader locates and loads the next stage of the boot process, such as a Memory Loader or a more advanced bootloader like U-Boot. 2. 𝐒𝐁𝐋/𝐌𝐋𝐎 (Memory Loader): A MLO/ SBL(Secondary Boot Loader) is a component responsible for loading the operating system kernel or bootloader from a specific memory location into the system's RAM (Random Access Memory). It often works in conjunction with the ROM Bootloader to facilitate the transition from non-volatile memory to volatile memory. Memory Loaders are commonly found in embedded systems and microcontrollers where booting directly from ROM may not be feasible due to limited resources or the need for flexibility in loading different software components. 3. 𝐔-𝐁𝐨𝐨𝐭 (Universal Bootloader): U-Boot is an open-source bootloader commonly used in embedded systems and Linux-based devices. It offers a flexible and extensible framework for initializing and booting a variety of hardware platforms. U-Boot supports multiple architectures, including ARM, MIPS, PowerPC, and x86, making it widely adaptable across different embedded systems. It provides features such as boot script support, environment variables, network boot capabilities, and interactive command-line interface, allowing developers to customize the boot process according to their specific requirements. U-Boot serves as a versatile and reliable bootloader solution for embedded devices, facilitating efficient system boot-up and software deployment. In summary, the ROM bootloader initiates the boot process by initializing hardware and locating the memory loader, which in turn loads the main bootloader or operating system kernel. U-Boot, as a versatile bootloader, offers extensive features and customization options for configuring and booting embedded systems and devices. https://lnkd.in/gJwWqaJu

A simple and clear explanation of the complete booting sequence for Embedded Linux, presented by Jegan Amirthalingam! Take a look to have an idea of the primary and secondary bootloader, and all further processes until the call to init! #embeddedsystems #linux #embeddedlinux

Linux is the only OS to support diagonal PC monitor mode — dev champions the case for 22-degree-rotation computing - Here's a fun tidbit — Linux is the only OS to support a diagonal monitor mode, which you can customize to any tilt of your liking. Latching onto this possibility, a Linux developer who grew dissatisfied with the extreme choices offered by the cultural norms of landscape or portrait monitor usage is championing diagonal mode computing. Melbourne-based xssfox asserts that the “perfect rotation” for software development is 22° (h/t Daniel Feldman). Xssfox devised a consistent method to appraise various screen rotations, working through the staid old landscape and portrait modes, before deploying xrandr to test rotations like the slightly skewed 1° and an indecisive 45°. These produced mixed results of questionable benefits, so the search for the Goldilocks solution continued. It turns out that a 22° tilt to the left (expand tweet above to see) was the sweet spot for xssfox. This rotation delivered the best working screen space on what looks like a 32:9 aspect ratio monitor from Dell. “So this here, I think, is the best monitor orientation for software development,” the developer commented. “It provides the longest line lengths and no longer need to worry about that pesky 80-column limit.” We note that Windows users with AMD and Nvidia drivers are currently shackled to applying screen rotations using 90° steps. MacOS users apparently face the same restrictions. Source: Linux is the only OS to support diagonal PC monitor mode — dev champions the case for 22-degree-rotation computing

The booting process of Embedded Linux is a streamlined sequence of steps that a device undergoes to load the Linux kernel and initialize the system. This process is tailored to the constraints and requirements of embedded systems, which often have limited resources and are designed for specific tasks. 🖋 Power-On and Hardware Initialization: When the device is powered on, the CPU begins executing instructions from a predefined location in the ROM. This initial code, part of the system's firmware, is responsible for basic hardware setup, such as initializing the clock, memory, and essential peripherals. 🖋 Primary Bootloader: The primary bootloader, a small piece of code in ROM, loads a more sophisticated secondary bootloader from a predefined storage location. This stage is minimal due to space constraints in ROM. 🖋 Secondary Bootloader: The secondary bootloader, like U-Boot, offers advanced features. It further initializes the hardware, sets up the memory map, and can load the kernel from various sources. This stage allows for configuration and customization of the boot process. 🖋 Loading the Kernel: The bootloader loads the Linux kernel into memory, decompressing it if necessary. It then passes control to the kernel, along with system information. 🖋 Kernel Initialization: The kernel initializes the CPU, memory, and hardware components, sets up subsystems, and mounts the root filesystem. 🖋 Init Process: The kernel starts the init process, the first user-space process, which is responsible for starting other processes and initializing the user-space environment. 🖋 User-Space Initialization: The init process executes scripts and launches services to set up the user environment, including network interfaces and system daemons. 🖋 Application Startup: Finally, control is handed over to the primary application(s) of the device, which may start automatically based on the system configuration. This process is highly customizable and varies across different embedded systems, tailored to the specific needs of each device. #embeddedlinux #embeddedsystems

How linux works Power On: Your journey starts with the push of that power button. The system comes to life, and the BIOS (Basic Input/Output System) kicks in, ensuring your hardware is in top shape. Master Boot Record: BIOS hands over control to the MBR on your hard disk, which then directs the boot loader to its designated spot. Boot loader: Picture the boot loader as the conductor, signaling for the kernel to take the stage. 4 Kernel: Ah, the kernel - Linux's heart and soul. It acts as the liaison between your hardware and the tasks you want to perform. 5 Initial RAM: The kernel settles into memory, and the system initializes with '/sbin/init' at the helm. 6 User Space: Now you're in control, with the shell and GUI ready to take your commands. Cycle of Operation: User Mode: You interact with the system, requesting programs or commands to run. System Mode: When tasks require more privilege, like hardware access, the kernel intervenes, managing requests securely. Kernel's Toolbox: Process Management: Handling the multitude of tasks you've got going. Memory Management: Allocating space for your applications and data. Device Drivers: Communicating with your hardware, from mouse to USB drive. System Calls: Special requests made by programs. File System Management: Organizing and storing your files securely. Brain of the Operation: The kernel communicates with CPU, memory, disk, and network to ensure smooth execution of your commands and programs.

New Post: Guide to Linux lscpu Command with Examples

How linux works Power On: Your journey starts with the push of that power button. The system comes to life, and the BIOS (Basic Input/Output System) kicks in, ensuring your hardware is in top shape. Master Boot Record: BIOS hands over control to the MBR on your hard disk, which then directs the boot loader to its designated spot. Boot loader: Picture the boot loader as the conductor, signaling for the kernel to take the stage. 4 Kernel: Ah, the kernel - Linux's heart and soul. It acts as the liaison between your hardware and the tasks you want to perform. 5 Initial RAM: The kernel settles into memory, and the system initializes with '/sbin/init' at the helm. 6 User Space: Now you're in control, with the shell and GUI ready to take your commands. Cycle of Operation: User Mode: You interact with the system, requesting programs or commands to run. System Mode: When tasks require more privilege, like hardware access, the kernel intervenes, managing requests securely. Kernel's Toolbox: Process Management: Handling the multitude of tasks you've got going. Memory Management: Allocating space for your applications and data. Device Drivers: Communicating with your hardware, from mouse to USB drive. System Calls: Special requests made by programs. File System Management: Organizing and storing your files securely. Brain of the Operation: The kernel communicates with CPU, memory, disk, and network to ensure smooth execution of your commands and programs.

Embedded devices often use special operating systems, such as 𝗙𝗿𝗲𝗲𝗥𝗧𝗢𝗦 and 𝗘𝗺𝗯𝗲𝗱𝗱𝗲𝗱 𝗟𝗶𝗻𝘂𝘅. How do you decide which one is the right fit for your application? 𝗙𝗿𝗲𝗲𝗥𝗧𝗢𝗦 is designed as a minimalist real-time operating system for microcontrollers, emphasizing simplicity and responsiveness. 𝗘𝗺𝗯𝗲𝗱𝗱𝗲𝗱 𝗟𝗶𝗻𝘂𝘅, on the other hand, is built on the Linux kernel, offering a feature-rich environment that supports complex applications, typically running on more powerful microprocessors. Our blog will guide you more on topic.

🚀 Layers of a Linux-Based Embedded System🚀 There are many layers that power Linux-based embedded systems? Let's discover them all. 💻🌐 1. Hardware Foundation:   - At its core, we have the hardware – the engine of innovation, comprising processors, memory, and various peripherals. 2. Bootloader Brilliance:   - The bootloader kicks things off, orchestrating the hardware's symphony and ushering in the Linux kernel. 3. Linux Kernel Magic:   - Behold the Linux kernel, the maestro conducting the orchestra. It manages resources, supports networking, and oversees processes with finesse. 4. Structured File Systems:   - Enter the file system, a meticulous organizer of data on storage devices. It lays the groundwork for the system's file hierarchy. 5. Root File System Rock:   - The root file system is the bedrock, housing crucial system files and directories – the essence of the entire structure. 6. Powerful System Libraries:   - Meet the supporting cast – system libraries like glibc, offering essential functions and services that applications rely on. 7. Middleware Marvels:   - Middleware steps in, providing abstractions and services. Think D-Bus for communication and ALSA for audio support. 8. Frameworks: Building Blocks for Apps:   - Application frameworks like Qt and GTK provide a structured environment for developing applications – the face of innovation. 9. End-User Bliss:   - It all culminates in user space applications – the web browsers, media players, and utilities that make our devices truly useful. 10. Init Systems:   - The init system takes the stage, initializing the system and managing processes. systemd and SysV init orchestrate this symphony. 11. Device Drivers Dance:   - Device drivers take a bow, enabling seamless communication between the kernel and hardware peripherals. 12. Network Stack Connection:   - Last but not least, the network stack facilitates connectivity, letting our devices communicate intelligently over networks. Understanding these layers opens the door to a world of possibilities in embedded systems. From processors to user-friendly applications, each layer plays a pivotal role in shaping our technological landscape. 🌐✨ These information are from ARM's course 👇🔍 #EmbeddedSystems #Linux #TechnologyExploration 🚀