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01_Introduction/README.md

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+# Chapter 1 – Introduction and Core Concepts
+
+## 🔧 What is System Programming?
+- Low-level programming that interacts directly with the **kernel** and system libraries via **system calls**, typically written in **C**.
+- Includes shell tools (bash, gcc, coreutils), daemons, webservers, etc.
+
+## Why Learn It?
+- Even in high-level environments (JS, Java, Python), understanding internal mechanisms leads to better, more efficient code.
+- Still essential for core components of Linux systems: kernel, drivers, glibc, gcc.
+
+## Core Elements
+1. **System calls** – entry points from user process to the kernel (e.g., `read()`, `write()`).
+2. **C Library** (glibc) – interface between user programs and system calls.
+3. **C Compiler** (gcc) – handles APIs, ABIs, and object formats.
+
+## API vs ABI
+- **API**: interface at the source code level (e.g., libc functions).
+- **ABI**: binary layout and conventions (e.g., syscall invocation, parameter ordering). Defines compatibility between systems and architectures.
+
+## Standards and Compatibility
+- POSIX/SUS as a reference, but Linux is not officially certified.
+- The **Linux Standard Base (LSB)** initiative extends POSIX/SUS to ensure binary compatibility across distributions.
+
+## Linux Basics
+- **Files**: name + inode, represented by **file descriptors** (int). Linear byte streams (no formatting).
+- **Processes**: entities with address space, pid, users, groups, permissions, signals.
+- **IPC**: inter-process communication mechanisms (pipe, FIFO, socket, shared memory, semaphores).
+- **Error handling**: functions return values and set `errno`. Useful functions: `perror()`, `strerror()`, `strerror_r()`.