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Dive into Linux Working

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Let's dive into Linux Working

Understanding the Linux Operating System: A Deep Dive

1. Kernel Initialization

The kernel is the heart of the Linux operating system. During boot, several critical steps occur:

  • BIOS/UEFI and Bootloader:

    • The BIOS or UEFI firmware initializes hardware components.
    • The bootloader (e.g., GRUB) loads the Linux kernel (vmlinuz).

  • Kernel Initialization:

    • The kernel initializes hardware devices (CPU, memory, storage, etc.).
    • It sets up essential data structures (e.g., process tables, page tables).
    • The root filesystem is identified and mounted.

2. Init Process

  • The kernel starts the init process (traditionally init, but modern systems use systemd).
  • Init is responsible for:
    • Starting system services and daemons.
    • Managing user sessions and spawning user-space processes.

3. User Space Initialization

  • Init spawns the first user-space process (usually init or systemd).
  • User sessions (e.g., graphical desktop environments) start from here.

4. Filesystem Hierarchy

  • Linux follows a standard directory structure:
    • /: Root directory.
    • /bin, /sbin: Essential system binaries.
    • /etc: Configuration files.
    • /home: User home directories.
    • /var: Variable data (logs, caches).
    • /tmp: Temporary files.
    • /usr: User programs and libraries.
    • /opt: Optional software.
    • /dev: Device files.
    • /proc: Virtual filesystem for process information.

5. Processes and Scheduling

  • The scheduler (e.g., Completely Fair Scheduler) manages process execution.
  • Processes are created using fork() and exec() system calls.
  • Priorities, nice values, and CPU affinity affect scheduling.

6. Memory Management

  • Virtual memory management:
    • Page tables map virtual addresses to physical memory.
    • TLB (Translation Lookaside Buffer) caches page table entries.
    • Demand paging and swapping optimize memory usage.
  • Memory allocation:
    • malloc(), free() manage dynamic memory.
    • Kernel memory management handles system memory.

7. File I/O and System Calls

  • File descriptors (stdin, stdout, stderr) facilitate I/O.
  • System calls (e.g., open(), read(), write(), close()) interact with files.

8. Networking

  • Network stack:
    • IP, TCP, UDP protocols.
    • Socket API for network communication.
  • Network configuration:
    • ifconfig, ip commands.
    • Routing tables determine packet forwarding.

9. Security and Permissions

  • Users, groups, and permissions control access.
  • sudo allows privilege escalation.
  • File integrity checks (e.g., md5sum, sha256sum) verify file integrity.

10. Device Drivers

  • Kernel modules manage hardware devices.
  • Examples: usb-storage, e1000 (Ethernet), i915 (graphics).

11. Logging and Debugging

  • syslog and dmesg provide system logs.
  • Debugging tools (e.g., strace, gdb) help diagnose issues.

12. Shutdown and Reboot

  • Init sends signals to processes.
  • Filesystems are unmounted.
  • The system halts or reboots.

🌟 Cheatsheet Linux🐧

  1. Linux Basics:

    • Commands:
      • ls: List files and directories.
      • cd: Change directory.
      • pwd: Print working directory.
      • cp: Copy files or directories.
      • mv: Move or rename files.
      • rm: Remove files or directories.
    • File Permissions:
      • chmod: Modify file permissions.
      • chown: Change file ownership.
      • chgrp: Change group ownership.
    • Processes:
      • ps: List running processes.
      • top: Monitor system processes.
      • kill: Terminate processes.
      • nice: Adjust process priority.
    • Package Management:
      • yum (RPM-based systems): Install, update, and manage packages.
      • apt-get (Debian-based systems): Similar functionality.

  2. File System Hierarchy:

    • Understand the directory structure:
      • /: Root directory.
      • /bin: Essential system binaries.
      • /etc: Configuration files.
      • /home: User home directories.
      • /var: Variable data (logs, caches).
      • /tmp: Temporary files.
      • /usr: User programs and libraries.
      • /opt: Optional software.
      • /dev: Device files.
      • /proc: Virtual filesystem for process information.

  3. Networking:

    • ifconfig or ip: Network configuration.
    • ping: Check network connectivity.
    • netstat: Network statistics.
    • ssh: Secure shell for remote access.
    • iptables: Firewall rules.

  4. Shell Scripting:

    • Create and execute shell scripts:
      • Variables.
      • Loops (for, while).
      • Conditionals (if, else).
      • Functions.
      • Input/output redirection.

  5. System Administration:

    • User management:
      • useradd, userdel, passwd.
    • Disk management:
      • df, du, mount.
    • Cron jobs:
      • crontab.

  6. Security:

    • sudo: Execute commands with superuser privileges.
    • File integrity checks:
      • md5sum, sha256sum.
    • Firewalls and SELinux.

Sharing working overview, and there's much more to explore!

Feel free to ask questions and share with beginners starting with AWS DevOps. Happy learning! 🌟🐧

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