Meet the cousins: Alma, Amazon Linux & more

This course uses Rocky and Ubuntu, the heads of the two big families. At work, and in the cloud, you'll also meet their cousins. The good news: once you know which family a distro belongs to, you already know 95% of it. This lesson covers the differences that trip people up.

The family tree

AlmaLinux: Rocky's twin

When CentOS Linux was discontinued, two free RHEL rebuilds took its place: Rocky Linux (started by one of CentOS's original founders) and AlmaLinux (backed by the company CloudLinux). For everything in this course they're identical: same dnf, same package names, same /etc/sysconfig, same firewalld and SELinux. Wherever a lesson says “Rocky”, it means Alma too.

• /etc/os-release says ID="almalinux", and /etc/almalinux-release replaces /etc/rocky-release.
• Rocky aims to match RHEL “bug-for-bug”. Since 2023, Alma aims to be “binary compatible” (programs built for RHEL run on it), which occasionally lets Alma ship a fix before RHEL does. You'll almost never notice.
• Alma is a popular container base image: almalinux:9, plus a tiny almalinux:9-minimal that uses microdnf, a small dnf without the extras. Rocky publishes images too: rockylinux/rockylinux:9.

Amazon Linux 2023: Red Hat family, with surprises

A common mix-up: Amazon Linux is not Debian-based. Amazon Linux 2023 (AL2023) is built from Fedora, so it uses dnf and .rpm, and its /etc/os-release says ID="amzn" and ID_LIKE="fedora". The older Amazon Linux 2 was based on CentOS 7 and reached end of life in June 2026, so migrate anything still running it. Things that surprise Rocky users on AL2023:

The AWS learning path (coming soon) will go deeper. The takeaway: dnf commands transfer, but check the “out of the box” assumptions.

Everyone else, side by side

Alpine is the container favorite because it's tiny, but it has no bash (only BusyBox sh, see lesson 14) and uses a different C library (musl), which occasionally breaks programs built for other distros. It gets a whole lesson of its own next: lesson 16.

Which one am I on?

Every one of them has /etc/os-release (Linux Basics, lesson 1). Scripts should look at ID_LIKE, not just ID. Then a script written for “rhel” also works on Rocky, Alma, Oracle and Amazon Linux without knowing their names:

#!/bin/sh
# which Linux family is this? (give an os-release file, or it reads this machine)
. "${1:-/etc/os-release}"
case "$ID $ID_LIKE" in
  *rhel*|*fedora*|*centos*) echo "$PRETTY_NAME: Red Hat family (dnf, .rpm)" ;;
  *debian*|*ubuntu*)        echo "$PRETTY_NAME: Debian family (apt, .deb)" ;;
  *alpine*)                 echo "$PRETTY_NAME: Alpine (apk)" ;;
  *)                        echo "$PRETTY_NAME: unknown family" ;;
esac

It's written in plain POSIX sh, so it runs even on Alpine.

Try it: the family detector 🧬

Your home folder has os-release/, real /etc/os-release files copied from AlmaLinux, Amazon Linux 2023, Debian and Alpine. Build a tool that sorts them into families.

Quick check