What is Linux?

Linux is a free, open-source operating system kernel first released by Linus Torvalds in 1991. When people say "Linux," they often mean a complete operating system built around this kernel—a Linux distribution (distro)—which includes the kernel, system libraries, user-space tools, and often a desktop environment.

Key characteristics

  • Open source: Source code is freely available; you can study, modify, and redistribute it.
  • Multi-user & multi-tasking: Many users and programs can run at the same time.
  • Portable: Runs on desktops, servers, embedded devices, and supercomputers.
  • Secure: User permissions, file ownership, and built-in security mechanisms.

The Linux Architecture

┌─────────────────────────────────────────────────────────┐
│  User applications (browsers, editors, scripts)         │
├─────────────────────────────────────────────────────────┤
│  Shell (Bash, Zsh) — command-line interface             │
├─────────────────────────────────────────────────────────┤
│  System libraries (glibc, etc.)                         │
├─────────────────────────────────────────────────────────┤
│  Kernel (process, memory, device, file system, network) │
├─────────────────────────────────────────────────────────┤
│  Hardware (CPU, RAM, disk, network)                      │
└─────────────────────────────────────────────────────────┘
  • Kernel: Manages hardware, memory, processes, and low-level system resources.
  • Shell: Text interface where you type commands; the default is often Bash.
  • User space: Everything that runs outside the kernel (programs, libraries, tools).

Common Linux Distributions

Distribution Typical use Package manager
Ubuntu Desktop, server, beginners apt / dpkg
Debian Stable base for many distros apt / dpkg
Fedora Cutting-edge, developer focus dnf
CentOS / Rocky Enterprise servers dnf / yum
Arch Linux Minimal, do-it-yourself pacman

This guide uses Ubuntu as the reference when discussing tools and examples.

The File System Hierarchy

Linux organizes everything as files under a single tree starting at root (/).

Path Purpose
/ Root of the file system
/home User home directories
/etc System configuration files
/usr User programs and libraries
/var Variable data (logs, caches, databases)
/tmp Temporary files
/bin, /usr/bin Executable commands
/sbin, /usr/sbin System administration commands
/dev Device files
/proc Virtual files describing processes and system info

Users, Groups, and Permissions

  • Every process and file is owned by a user and a group.
  • root (user ID 0) has full administrative access.
  • Use sudo to run individual commands as root when needed; avoid logging in as root for daily work.

Basic permission concepts

  • Read (r): View file contents or list directory.
  • Write (w): Modify file or add/remove files in directory.
  • Execute (x): Run file as program or enter directory.

Permissions are shown in groups of three: owner, group, others (e.g. rwxr-xr--).

Why Use Linux?

  • Stability and performance on servers and long-running systems.
  • No license cost for the OS itself.
  • Flexibility: Choose your distro, desktop, and tools.
  • Scripting and automation via shell and other languages.
  • Wide use in cloud, containers (Docker, Kubernetes), and embedded systems.

Next Steps