## TL;DR

Linux is an open-source, Unix-like operating system kernel created by Linus Torvalds in 1991. Combined with GNU utilities, it forms the GNU/Linux operating system that powers 100% of the TOP500 supercomputers, 96.3% of the top 1 million web servers, all Android devices (3+ billion), and the majority of cloud infrastructure (AWS, GCP, Azure). Linux is licensed under GPLv2 and maintained by thousands of contributors worldwide, with Linus Torvalds remaining the principal maintainer as of 2026.

## Core Concepts

- **Kernel**: Core OS component managing hardware, processes, memory, and I/O
- **Distributions**: Complete OS packages (Ubuntu, Debian, RHEL, Arch, Fedora) combining kernel + GNU tools + package manager
- **Shell**: Command-line interface (bash, zsh, fish)
- **Package Management**: apt (Debian/Ubuntu), dnf (Fedora/RHEL), pacman (Arch)
- **Filesystem Hierarchy Standard (FHS)** : Standardized directory structure (`/bin`, `/etc`, `/var`, `/home`)
- **Systemd**: Init system and service manager (default on most distros since ~2015)

## Linux in Production

- **Cloud**: 96%+ of cloud workloads run on Linux (AWS EC2 Linux, GCP, Azure Linux VMs)
- **Containers**: Docker runs on Linux kernel features (namespaces, cgroups)
- **Embedded**: Android (Linux kernel), IoT devices, routers, automotive (Automotive Grade Linux)
- **Supercomputing**: 100% of TOP500 since 2017

## Further Reading

- [Kernel.org Docs](https://www.kernel.org/doc/html/latest/): Official Linux kernel documentation
- [Linux Kernel Source](https://github.com/torvalds/linux): Torvalds' GitHub mirror