system-programming/01_Introduction/README.md

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().