# k1.1 — Distributions & Families: What “Linux” Is (and Isn’t) 🌍

### What people mean when they say “Linux”

In everyday dev/admin talk, “Linux” usually refers to an *entire operating system stack*, not just one component:

1. **Linux kernel**  
    The core that handles:
    
    
    - processes and scheduling
    - memory management
    - networking
    - hardware drivers
2. [**Userland tools**](https://wiki.fabula.vision/books/linux/page/common-linux-command-line-tools-portable-across-distros "Common Linux Command-Line Tools (Portable Across Distros) 🧰")  
    The standard command-line tools you’ll use constantly, such as:
    
    
    - `ls`, `cp`, `mv`, `rm`, `find`
    - `grep`, `sed`, `awk`
    - `tar`, `ssh`, `curl`
3. **Init / service manager**  
    On most modern distros, this is **systemd** (so services behave similarly across many distributions).
4. **Package manager + repositories**  
    How software is installed and updated (this is one of the biggest practical differences across distros).
5. **Defaults & policies**  
    Security frameworks, filesystem defaults, preinstalled tools, and “the distro’s way” of doing common tasks.

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### What a “distribution” actually is

A **Linux distribution (distro)** is a curated bundle of the components above, plus:

- a release philosophy (stable vs fast-moving)
- a packaging system and official repositories
- default configuration choices
- documentation/community norms

So you’re not learning a completely different OS each time—you’re learning **the same core concepts** with different “packaging and defaults.”

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### The main families you’ll encounter (server/web world)

For web development and WordPress hosting, these families matter most:

1. **Debian family**
    
    
    - **Debian** (very stability-focused, conservative updates)
    - **Ubuntu** (based on Debian; very common, especially **Ubuntu LTS** on servers)
    - Typical traits: 
        - uses **APT** (`apt`)
        - huge ecosystem of tutorials and packages
2. **RHEL family** (Red Hat Enterprise Linux–compatible)
    
    
    - **Rocky Linux**, **AlmaLinux** (common for enterprise-style servers and some tooling stacks)
    - Typical traits: 
        - uses **DNF** (`dnf`, historically `yum`)
        - **SELinux** is commonly enabled and relevant

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### What’s shared across most distros (the “learn once” core)

If you learn these well, you can function on almost any mainstream Linux server:

- filesystem concepts and common directories (you’ll cover this in **k3**)
- permissions and ownership (`chmod`, `chown`)
- processes and signals (`ps`, `kill`)
- service management concepts (often via `systemctl`)
- networking basics (ports, DNS, `curl`, `ss`)
- SSH and key-based access

---

### What this means for your course goal

Your plan—**learn cross-distro fundamentals first without committing**—works because:

- the *core Linux skills* transfer extremely well
- later, you mainly “translate”: 
    - `apt` ↔ `dnf`
    - AppArmor ↔ SELinux
    - UFW ↔ firewalld
    - slightly different defaults/paths

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### Tiny self-check ✅

Answer these without Googling (it’s fine if you can’t yet):

1. What’s the **kernel** responsible for (in one sentence)?
2. Name **two things** that are usually different between Debian-based and RHEL-based distros.
3. What’s one Linux skill that should transfer across almost all distros?

If you want, reply with your answers and I’ll correct/clarify briefly.