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! 🌟🐧