Added Day 02 Linux architecture notes

2026/day-02/linux-architecture-notes.md

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+1) Core Components of Linux
+
+Kernel
+
+The main part of Linux.
+
+Talks directly to hardware (CPU, memory, disk, devices).
+
+Manages processes, memory, files, and networking.
+
+User Space
+
+Where users and applications work.
+
+Includes commands, tools, shells, and programs.
+
+Example: bash, ls, cp, apps, scripts.
+
+init / systemd
+
+First process that starts when system boots.
+
+Starts and manages all system services.
+
+systemd is the modern init system used in most Linux systems.
+
+2) How Processes Are Created & Managed
+
+A process is created when we run a command or program.
+
+Linux uses fork() to create a new process and exec() to run a program.
+
+Kernel manages:
+
+CPU time
+
+Memory
+
+Scheduling
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+Process priority
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+Process States
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+Running (R) – Process is using CPU.
+
+Sleeping (S) – Waiting for input or event.
+
+Stopped (T) – Paused manually.
+
+Zombie (Z) – Process finished but not cleaned by parent.
+
+3) What systemd Does & Why It Matters
+
+Manages system services like:
+
+Network
+
+SSH
+
+Docker
+
+Web servers
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+Starts services in correct order.
+
+Automatically restarts failed services.
+
+Makes boot faster and system stable.
+
+4) 5 Linux Commands I Use Daily
+
+ls – list files and folders
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+cd – change directory
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+pwd – show current location
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+ps – check running processes
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+top / htop – monitor system usage