Day 4 - Distributions: The Unit That Bundles the Kernel and Tools for Sale

📌 Key Takeaways

• Distribution = Linux kernel + GNU tools + package manager + installer + application software.
• The three major families: Red Hat family (RPM), Debian family (DEB), and SUSE family (RPM).
• You tell families apart by package format — RPM is Red Hat and SUSE, DEB is Debian and Ubuntu.
• Stability flows Fedora → RHEL → CentOS/Rocky/Alma. Fedora is the testing ground.
• Android is also based on the Linux kernel, but it doesn't use the GNU tools, so it differs from ordinary distributions.

What Is a Distribution?

With only a kernel, you can't use a computer. To actually use one, you need all of this in addition.

• Every distribution uses the very same kernel (only the version differs).
• What sets distributions apart are package format, management tools, default settings, and support policy.

The Three Major Families

Trap: SUSE also uses RPM. If you memorize only "RPM = Red Hat," you'll be wrong. It's safer to tell them apart by the high-level tool — dnf means Red Hat, zypper means SUSE.

How Low-Level and High-Level Tools Differ

The reason the tools are split into two columns in the table is dependencies. A single program usually needs several other libraries installed in order to run.

Here is how you type the same job in each family, side by side (detailed options are covered in Week 7).

• The relationship between yum and dnf: dnf is the successor to yum. From RHEL 8, dnf is the default, and the yum command remains for compatibility and links to dnf.
• The relationship between apt and apt-get: apt came later and is polished to be friendlier for humans. They do the same job.

⚠️ Trap: On the Debian family, apt update only refreshes the repository lists. Actually upgrading packages is apt upgrade. On the Red Hat family, dnf update actually upgrades packages. Even with the same name, they do different things.

Red Hat Family

   Fedora  ──────►  RHEL  ──────►  CentOS Stream / Rocky / Alma
 (testing ground)  (commercial     (free RHEL-compatible
                    stable)          versions)
  Latest tech       Paid support    Free rebuilds
  Fast cycle        Long-term support

• Fedora: A testing ground that tries new technologies first. Short cycles and big changes.
• RHEL (Red Hat Enterprise Linux): A commercial distribution that contains what was proven in Fedora. Paid technical support is the product.
• CentOS: Used to be a free version that rebuilt the RHEL source as-is. In 2021 the policy changed and it became CentOS Stream (upstream of RHEL), and Rocky Linux and AlmaLinux filled the gap it left.

The diagram above simplifies the "direction stability flows," and the actual order in which code flows is a bit finer.

   Fedora  ──►  CentOS Stream  ──►  RHEL  ──►  Rocky Linux · AlmaLinux
 (experiment)   (previews the next   (commercial)  (free versions rebuilt
                 RHEL version)                       to be compatible with RHEL)

• The old CentOS sat after RHEL (it rebuilt RHEL as-is). CentOS Stream sits before RHEL (it receives what will go into the next RHEL first). The name continued, but the position is exactly the opposite.
• So the old CentOS's role as a "free version identical to RHEL" is now taken over by Rocky and Alma.

Debian Family

• Debian: Built by a non-profit community. It puts stability first, so its packages are conservative.
• Ubuntu: Built by Canonical on a Debian base. It has good desktop usability, and LTS (long-term support) versions are supported for 5 years.
• Linux Mint: Based on Ubuntu. It offers a more familiar desktop.

Debian runs three branches at the same time.

Ubuntu's version number is the release year and month.

   22.04 LTS        23.10          24.04 LTS
   │  │             │  │           │  │
   │  └ April        │  └ October    │  └ April
   └─── 2022         └─── 2023       └─── 2024

• A new version comes out every 6 months (April and October), and every 2 years the April version of the even-numbered year becomes the LTS.
• Non-LTS regular versions are supported for only 9 months, so servers use the LTS.

SUSE Family

• SLES (SUSE Linux Enterprise Server): A commercial distribution. Strong in Europe.
• openSUSE: The free community edition. Its hallmark is an integrated configuration tool called YaST.

Other Things to Know

Past exams include questions asking for "an operating system based on the Linux kernel" with Android among the options. Android is a separate layer made by Google on top of the Linux kernel, so it shares only the kernel and its composition differs from ordinary distributions.

Who Came from Whom

Most distributions were not built from the ground up but on top of an earlier distribution. Questions asking you to pick "the one with a different base" come from this family tree.

Distributions outside Red Hat, Debian, and SUSE each have their own package tools too.

Checking the Distribution You're Using

uname only tells you about the kernel. The distribution is told by files under /etc.

$ cat /etc/os-release
NAME="Rocky Linux"
VERSION="9.3 (Blue Onyx)"
ID="rocky"
ID_LIKE="rhel centos fedora"
VERSION_ID="9.3"
PRETTY_NAME="Rocky Linux 9.3 (Blue Onyx)"
 
$ cat /etc/redhat-release
Rocky Linux release 9.3 (Blue Onyx)

• The ID_LIKE line tells you the family. Rocky shows rhel centos fedora, and Ubuntu shows debian. When you meet an unfamiliar distribution, look at this line first.
• If you use a wildcard like cat /etc/*-release, whatever distribution it is, all the matching files come out at once.

Commonly Mistaken Points

1. "If it uses RPM, it's the Red Hat family" → SUSE is RPM too. If you see zypper or YaST, it's SUSE.
2. "Ubuntu is the Red Hat family" → It's the Debian family. Mint also reaches Debian by way of Ubuntu.
3. "Fedora is a free rebuild of RHEL" → It's the opposite. Fedora sits before it, and RHEL is built from it. The rebuilds are Rocky and Alma.
4. "Each distribution has a different kernel" → The kernel is the same Linux kernel; only the version and configuration differ.
5. "A rolling release is the most stable" → It means always up to date, not stable. Stability lies with fixed releases and LTS.

Release Models

Which Distribution Should You Pick?

• Servers and enterprise environments → RHEL, Rocky, AlmaLinux, SLES (long-term support and stability)
• Personal desktop and beginners → Ubuntu, Linux Mint (easy to install and use)
• Experimenting with the latest technology → Fedora, Arch
• Study and certification prep → Ubuntu or Rocky. It's good to get hands-on with both families

That's all for this week. Tomorrow we tie together the concepts covered in Week 1 on a single page.

📖 Glossary

• Distribution : The kernel, GNU tools, package manager, and applications bundled together into something installable.
• Package manager : A tool that manages software installation, removal, and dependencies. dnf, apt, zypper, etc.
• RPM : The package format used by the Red Hat and SUSE families, and also its management command.
• DEB : The package format used by the Debian and Ubuntu families.
• RHEL : Red Hat's commercial enterprise distribution. Paid technical support is the core product.
• Fedora : A community distribution that tests technologies destined for RHEL first.
• LTS : Long Term Support. A policy of maintaining a particular version for a long time.
• Rolling release : A distribution model that keeps updating to the latest state with no version divisions. Arch is the classic example.