Ubuntu, RHEL, CentOS Stream, Rocky or Alma: picking a server Linux after CentOS

For more than a decade, the default answer for "free, stable Linux server" in many companies was CentOS: a free rebuild of Red Hat Enterprise Linux (RHEL), binary compatible, supported for years. That answer no longer exists. CentOS Linux 8 ended on 31 December 2021, earlier than originally planned, and CentOS Linux 7 reached end of life on 30 June 2024.

We still meet teams running CentOS 7 machines that "just work." They get no security updates. This post explains, without assuming deep Linux knowledge, what replaced CentOS and how to choose.

What happened to CentOS

Red Hat moved the CentOS project to CentOS Stream. The important difference is its position in the release flow:

• Old CentOS Linux came after RHEL: Red Hat released RHEL, then CentOS rebuilt the same code for free.

• CentOS Stream comes before the next RHEL minor release: it is where changes land first, and RHEL is built from it.

So CentOS Stream is not "free RHEL." It is a continuously updated preview of the next RHEL update. It is stable enough for many uses, and Red Hat and companies like Meta use it, but it moves more often than a classic enterprise release.

In 2023 Red Hat also changed how it publishes RHEL source code, limiting public access mainly to CentOS Stream. That pushed the community rebuilds to change their methods, which we cover below.

The options

Red Hat Enterprise Linux (RHEL)

The commercial original. You pay for a subscription and get:

• A long life cycle: about ten years per major version (full support, then maintenance), with paid extended life options after that.

• Vendor support, security response and certifications. Many enterprise applications (SAP, databases, security tools) are certified on RHEL specifically.

• Tools such as Red Hat Insights and Satellite for managing fleets.

Red Hat also offers a no-cost Developer Subscription for individuals, covering a limited number of systems, and programs for small production use. Check the current terms on Red Hat's site.

CentOS Stream

Free, upstream of RHEL. Good for building and testing against the next RHEL, for contributors, and for infrastructure that can follow frequent updates. Each Stream version has a shorter life than the matching RHEL version, roughly five years. Not ideal if you need to run the same version for a decade.

Rocky Linux and AlmaLinux

Free community distributions created after the CentOS change, both aiming to be drop-in replacements for RHEL.

• Rocky Linux, started by one of the original CentOS founders, aims for bug-for-bug compatibility with RHEL.

• AlmaLinux, backed by a foundation, now aims for ABI compatibility (software built for RHEL runs on it) while allowing itself to ship some fixes RHEL has not.

Both follow RHEL's major versions and support periods closely, and both provide tools to migrate from CentOS 7 or 8. For most teams that loved CentOS for being "free RHEL," one of these two is the closest replacement. Choose based on community, mirror availability in your region, cloud images and support vendors you trust.

Ubuntu Server LTS

A different family (based on Debian), made by Canonical.

• A new LTS (long-term support) release every two years in April, with five years of standard security updates.

• Ubuntu Pro extends security coverage to ten years and covers many more packages. It is free for personal use on a small number of machines, and paid for businesses. Canonical also sells a Legacy add-on for even longer coverage.

• The most common Linux on public clouds, with official images everywhere and huge community documentation.

Moving from CentOS to Ubuntu is a bigger change than moving to Rocky or Alma: different package manager (apt instead of dnf/yum), different file locations and different security tooling (AppArmor by default instead of SELinux).

Debian

The community distribution Ubuntu is built on. Very stable, free, no company behind it, about five years of combined support per release with the LTS effort. A solid choice for teams comfortable without a commercial vendor.

Side-by-side

How to choose

1. Do you need vendor support or certifications? If an auditor, a contract or a vendor requires it, choose RHEL (or Ubuntu Pro if your software is certified there).

2. Are you migrating CentOS servers with minimal change? Rocky Linux or AlmaLinux. The commands, configuration files and SELinux policies stay the same.

3. Is your team cloud-first and container-heavy? Ubuntu LTS is often the easiest path, with the most images, guides and integrations.

4. Do you build software for future RHEL releases? Use CentOS Stream in CI to catch issues early.

5. What does your team already know? The cheapest distribution is the one your on-call engineers can fix at night.

If you still run CentOS 7 or 8

Treat it as urgent. These systems receive no security patches, and attackers scan for known vulnerabilities in old versions of software such as OpenSSH, OpenSSL and the kernel.

A safe migration order:

1. Inventory: list every CentOS machine, what runs on it and who owns it.

2. Isolate: restrict network access to old machines while you migrate.

3. Rebuild rather than upgrade in place where you can: create a new server with your new distribution, deploy the application with automation, test, then switch traffic.

4. Use official migration tools only where rebuilding is impractical, and take a full backup first. Rocky and Alma document their conversion tools; Red Hat offers paid extended support for CentOS 7 through some partners and its own conversion path to RHEL.

5. Test the application, not just the boot: library versions differ between major releases.

Containers change the question, but do not remove it

Many teams now ship applications as containers, and ask whether the server OS still matters. It matters less, but not zero. Two separate choices exist:

• The host OS that runs the container engine or Kubernetes nodes. It needs security updates, a supported kernel and good integration with your cloud or hardware. Managed Kubernetes services often choose it for you.

• The base image inside each container. Red Hat publishes Universal Base Images (UBI) that can be freely redistributed, Canonical publishes Ubuntu images, and Debian, Rocky and Alma publish their own. The base image decides which libraries your app uses and who sends you security fixes for them.

They do not have to match. A common setup is Ubuntu or a cloud-provided OS on the host and a slim Debian, Ubuntu or UBI image in the container. What matters is that both layers stay supported and are rebuilt regularly, so fixes actually reach production.

Key takeaways

• CentOS Linux 7 and 8 are end of life; CentOS Stream is the upstream preview of RHEL, not a free copy of it.

• Rocky Linux and AlmaLinux are the closest free replacements for classic CentOS.

• RHEL is the choice when you need vendor support, certifications and the longest life cycle.

• Ubuntu LTS is the most common cloud server OS and offers ten-year coverage with Ubuntu Pro.

• Pick the system your team can operate confidently, then automate its builds.

References

• CentOS project: end dates

• CentOS Stream

• Red Hat Enterprise Linux life cycle

• Red Hat Developer Subscription for Individuals

• Ubuntu release cycle

• Rocky Linux

• AlmaLinux

• Debian releases