Distributions

“Linux” is a kernel, not an operating system. The kernel at kernel.org handles process scheduling, memory management, device drivers, the syscall interface, and nothing else. It does not include a shell, a text editor, a package manager, or a C library. To get a usable system you need userland — and that is what a distribution provides.

The userland layer almost universally includes:

• GNU coreutils — ls, cat, cp, grep, awk, bash and ~100 other essential utilities
• glibc (or musl for minimal images) — the C standard library that every compiled program links against
• A package manager — the mechanism for installing, updating, and removing software
• Defaults and configuration — which init system, which default editor, which network manager, which security policy

The kernel is a small fraction of what you actually interact with day to day.

The Debian/Ubuntu family uses .deb packages and apt. Debian is the parent — known for stability and a very long release cycle (roughly two years between major releases, then multi-year security support). Debian stable is conservative: packages are old but battle-tested.

Ubuntu is a Debian derivative that ships every six months (LTS releases every two years with five years of security support). Ubuntu made Linux palatable for desktop use and is now the dominant choice for cloud servers. When you provision an EC2 instance and pick “Ubuntu 24.04”, you are getting the Debian ecosystem with Ubuntu defaults.

# Debian/Ubuntu package operations
sudo apt update           # refresh the package index
sudo apt install nginx    # install a package
sudo apt upgrade          # upgrade all installed packages
dpkg -l nginx             # inspect an installed package

The RHEL/Fedora family uses .rpm packages and dnf. Red Hat Enterprise Linux (RHEL) is the commercial, enterprise-support product. Fedora is the upstream playground where new features land first before being hardened into RHEL. CentOS was a free RHEL rebuild; after its end-of-life, AlmaLinux and Rocky Linux took its place.

The RHEL family dominates regulated industries (finance, healthcare, government) because Red Hat provides long-term commercial support contracts and FIPS-certified builds. When you see “RHEL 9”, that is a ten-year support commitment with a single kernel version that gets backported security patches rather than version bumps.

# RHEL/Fedora package operations
sudo dnf install nginx    # install a package
sudo dnf update           # upgrade all installed packages
rpm -qi nginx             # query an installed package

The package format (.rpm vs .deb) is the most visible difference, but the deeper difference is the support model and update philosophy.

Arch Linux is the rolling-release extreme. There is no “Arch 2024” — you install once and the system updates continuously to the latest upstream versions. Packages arrive hours after upstream releases. This means cutting-edge software and frequent breakage — useful for developers who want new kernel features, not for production servers.

Arch also has near-zero defaults: no installer GUI, no pre-configured services, no predefined user. You build the system you want from scratch. Its value is pedagogical as much as practical: you learn exactly what each component does because you chose it explicitly.

# Arch package operations
sudo pacman -Syu          # update the whole system
sudo pacman -S nginx      # install a package

Manjaro and EndeavourOS are Arch derivatives that add an installer and saner defaults.

What is identical across all distros. The Linux kernel itself — the same binary from kernel.org — behaves identically regardless of which distro ships it. A bash script that uses only POSIX features and standard GNU tools runs on all of them without modification. Syscalls are stable: code that calls read() and write() compiled on Debian runs on RHEL without recompilation (the ABI is guaranteed). Systemd is the init system on all major distros. /proc and /sys expose the same kernel data everywhere. The knowledge in this track is distro-portable; we will call out the few places where it is not.