AlmaLinux vs. Rocky Linux: Exploring the Key Differences

With the 2020 decision to discontinue CentOS Linux came two new Enterprise Linux distributions to fill the void: AlmaLinux, backed by CloudLinux; and Rocky Linux, driven by one of the creators of CentOS Linux, Gregory Kurtzer. Now with both boasting several successful releases, and both ready for use in enterprise deployments, comparing AlmaLinux vs. Rocky Linux is a worthwhile exercise for teams considering Enterprise Linux distributions in the post CentOS EOL era.

In this blog, I provide an in-depth comparison of AlmaLinux vs. Rocky Linux across all aspects of the two distros, including everything from community and sponsorship, to image availability, release lag and enterprise support providers.

AlmaLinux vs. Rocky Linux

The main difference between AlmaLinux vs. Rocky Linux is their development process due to Red Hat's recent restrictions to RHEL source code. Rocky Linux still uses RHEL SRPMs for their upstream, whereas AlmaLinux's applications are built to run on RHEL and RHEL-based systems, but it is not an exact clone of RHEL. 

In June 2023, Red Hat announced that they would no longer publish the RHEL source code in favor of only releasing the CentOS Stream source code, which can be different than what is officially packaged in Red Hat Enterprise Linux.

This threw the RHEL-rebuild distros for a loop and Rocky Linux and AlmaLinux developed different solutions to this change.

Rocky Linux originally stated on their website that they are “designed to be 100% bug-for-bug compatible with Red Hat Enterprise Linux” and this has not changed as the original RHEL SRPMs continue to be used as the upstream for Rocky Linux.

AlmaLinux took a different approach, though, and the claim on its website that AlmaLinux is “1:1 binary compatible with RHEL and pre-Stream CentOS” has been replaced with “AlmaLinux OS is binary compatible with RHEL” which allows AlmaLinux to run applications built to run on RHEL and RHEL-based systems, but relieves them of publishing an exact clone of RHEL.  

Community and Sponsorship

The Rocky Enterprise Software Foundation (RESF) is a Public Benefit Corporation created by CentOS Linux co-founder Gregory Kurtzer “to organize a community around enterprise, research, academia, individuals, and other institutions” specifically for Rocky Linux. The RESF is made up of team leads and other individuals from within the Rocky Linux community for the purpose of transparency and mitigating the possibility of an individual or external entity taking control of the project.

RESF invites sponsors and partners to contribute to Rocky Linux with a current balance of 11 sponsors, 13 partners, and 3 support providers as listed on the Rocky Linux website. Gregory Kurtzer’s CIQ is the founding sponsor, the founding partner, and a support partner for Rocky Linux.

AlmaLinux is provided by the AlmaLinux OS Foundation, a 501(c)(6) non-profit established to “(i) further develop and maintain AlmaLinux OS as a no registration, ad free, stable, open source Linux distribution for the benefit of and free use by the general public, (ii) facilitate and promote the growth of a community of vendors and partners delivering solutions based on or complimentary to AlmaLinux OS, and (iii) undertake such other activities which its Board of Directors may from time to time approve.” The Foundation consists of Contributor Members, Mirror Members, Sponsor Members, and Alumnus Members.

Per the AlmaLinux Wiki, the foundation includes over 400 individual members, over 100 Mirror sponsors, and over 25 Corporate sponsors. CloudLinux is AlmaLinux’s founding company, providing $1 million in sponsorship annually.

Popularity / Adoption

None of the following numbers are indicative of a clear winner by themselves. As mentioned above, there are different reasons why one distribution or another may be the best for a particular deployment. For more data on enterprise Linux distributions and their usage, check out the most recent State of Open Source Report. 

Distrowatch

Looking at the trending data for the last 12 months shows a good trendline for popularity for the distributions (based on page hits on distrowatch.com).

Here's what we see looking at rankings from a year ago, 6 months ago, 3 months ago, and this month:

Cloud Provider Marketplace Images

Let’s look at the three largest cloud providers in terms of image demand: AWS, Azure, and Google Cloud. All three cloud providers have official and 3rd party images available for both AlmaLinux and Rocky Linux.

AWS

On AWS, AlmaLinux and Rocky Linux both have official offers for AlmaLinux 8, 9, and 10 for x86_64 and arm64. There are approximately 496 total AlmaLinux offers and 588 total Rocky Linux offers, mostly from 3rd party publishers.

Azure

On Azure, AlmaLinux has official offers for AlmaLinux 8, 9, and 10 (both x86_64 and arm64) as well as an offer for AlmaLinux 8 HPC (x86_64). Rocky Linux has official images for Rocky Linux 8 and 9 (both x86_64) on Azure. There are many, many 3rd party offers for both (Azure’s marketplace search doesn’t restrict to the search term, thus non-Rocky and non-Alma results are returned so getting an accurate number is difficult).

Google Cloud

Google Cloud lists an official AlmaLinux 8 and 9 product, 20 3rd party AlmaLinux products, an official Rocky Linux 8 and 9 product, and 51 3rd party products.

On-Premise Images

AlmaLinux and Rocky Linux offer on-premise images in their repositories.

AlmaLinux offers a multitude of GenericCloud, GenericCloud-UEFI, and OpenNebula images for AlmaLinux 8, 9, and 10 for x86_64, aarch64, s390x, and ppc64le.

Rocky Linux offers an even wider variety of images, including Azure, Container, EC2, OCP, GenericCloud, QEMU and WSL images (plus a couple of SBC, aka Single Board Computer, images) for Rocky Linux 8 (aarch64 and x86_64), 9 (aarch64, ppc64le, s390x and x86_64) and 10 (aarch64, ppc64le, riscv64, s390x and x86_64).

Hashicorp’s Vagrant Cloud has listings for both distros, too. Searching for “AlmaLinux” returns 8 pages of results with the 6 official AlmaLinux 8, 9, and 10 boxes supporting hyperv, libvirt, parallels, virtualbox, and vmware_desktop with a combined download count that exceeds 190,000.

A search for “RockyLinux” returns 6 pages of results with the 3 official Rocky Linux 8, 9, and 10 boxes supporting libvirt, virtualbox, and vmware_desktop with a combined download count around 89,000.

Outside of the official releases, 3rd party box publishers make up the majority of the available boxes, including popular box publishers like bento, boxomatic, and OpenLogic.

In addition to on-premises vagrant boxes for virtualbox and vmware_desktop, OpenLogic also publishes boxes which allow vagrant to manage cloud-based virtual machines on AWS, Azure, and Google. Hashicorp doesn’t provide granular, per-environment usage counts, but they do provide a total download count. OpenLogic’s AlmaLinux and Rocky Linux images currently have almost identical download counts. 

Docker Images

The official Docker images for AlmaLinux and Rocky Linux both exceed 10 million downloads. By pulls alone, Rocky Linux is leading by about 13% (or 11K+ downloads) over the last week. 
 

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Rocky Linux Support  AlmaLinux Support   Hardened Images

Development Process

Rocky Linux and AlmaLinux both have minor differences in how they develop their distributions, including differences in build systems and architecture support.

Upstream

AlmaLinux and Rocky Linux both utilize source code from Red Hat as their upstream, but each goes about it a little differently.

AlmaLinux’s goal of now being “RHEL binary/ABI compatible” offers more flexibility on where source code comes from since duplicating RHEL exactly is no longer paramount. I was unable to find record of exactly where the source code/patches are now pulled from, but an article published by AlmaLinux states they are using “several sources.”

Rocky Linux utilizes at least two methods of obtaining the RHEL source code in order to continue to strive to be “100% bug-for-bug compatible.” One method is using RHEL UBI (Universal Base Image) containers and the other is launching pay-per-use cloud instances, both of which provide legitimate access to the Red Hat source.  

These changes have all been after RHEL 8.8 and 9.2 were released so we haven’t yet seen what will happen when the next minor version (or major version, for that matter) of RHEL is released. Chances are that we will see variations in expected release lag (see below) but that’s purely conjecture.

Build Systems

AlmaLinux and Rocky Linux are both built using their own build systems.

AlmaLinux utilizes a custom AlmaLinux Build System (ALBS) to produce their assets. I couldn’t find any hard information about when AlmaLinux started to use this build system, or if they were using it from the start, but the first build on build.almalinux.com is from Sept 15, 2021, so I think I can safely assume that AlmaLinux 8.6 and 9.0 were built with ALBS, but earlier releases may have been also.

Prior to Rocky Linux 9.0, the Rocky Release Engineering team used Koji (and other Fedora components) to build Rocky Linux. Starting with Rocky Linux 9.0, the build system has been replaced with Rocky’s own Peridot. It was the change of build system which induced a lot of the release lag for RL 9.0, which we’ll talk about in a bit.

Architecture Support

x86_64 support was the first platform that both distros released, and both now support aarch64, ppc64le, s390x, and x86_64 with their 9.0 releases.

Starting with AlmaLinux 8.4, aarch64 support was added, AL 8.5 added ppc64le, AL 8.6 offered s390x support, and AL 9.0 introduced s390x support.

In contrast, Rocky Linux included support for aarch64 from the start, but didn’t include support for ppc64le or s390x until RL 9.0.

RHEL 10.0 introduced yet another x86 restriction:  x86_64 releases would now require systems with least x86_64_v3 support (2015 Intel Haswell/AMD Excavator or newer). 

AlmaLinux decided to build AL 10 in both x86_64_v3 (listed as just “x86_64”) and x64_64_v2  (listed as “x64_64_v2”) which will facilitate using older systems with their latest 10 release. 

Release Lag

There are two types of release lag that I like to keep an eye on, initial release lag and update release lag.

Initial Release Lag

The first is initial release lag. Typically, this applies to major releases, but since both AlmaLinux and Rocky Linux joined the RHEL rebuild party mid-EL8.x, it also applies to minor releases.

AlmaLinux was the first of the RHEL rebuilds to receive a GA release with AlmaLinux 8.3 published on Mar 26, 2021.

As mentioned earlier, the entire Rocky Linux build system was swapped out for RL 9.0, which explains the higher release lag for RL 9.0. Now that Peridot is in production, it will be used to build all future Rocky Linux releases.

Regardless, for the last two minor releases, both AlmaLinux and Rocky Linux have had minimal wait times after RHEL was published.

Update Release Lag

The second type of release lag is update release lag. This is the lag between when Red Hat publishes a package update and when the RHEL rebuild distribution releases their package update.

With so many updates to consider, I’m going to look at just a couple of the kernel updates to get a sample of expected release lag. The timestamps I am using for comparison are the file dates on my local mirror.

As we can see, from the 8.4 to the 8.7 releases, the update release lag was minimal for both distributions, with a typical lag of a day or less after Red Hat publishes the update for RHEL. There has been a little more variability in the release lag starting with the 8.8 release and with some of the 9.x releases, but the lag is still generally less than we’ve seen with CentOS Linux 7.  

Feature Inclusion

The features included with both distributions should be the same. Looking at the repos that each distribution offers, the same basic repositories are present.

Where they differ is that Rocky Linux provides a ‘devel’ repo which contains packages that are required for building other packages.

Otherwise, the package offerings for both AlmaLinux 8.8 and Rocky Linux 8.8 are nearly identical with both repos containing around 6850 RPMs. The same is seen with AL 9.2 and RL 9.2 with approximately 5880 RPMs published by both. Most of the changes are optional packages built from the same specfile or distro-specific packages. With 9.6 and 10.0, both distributions offer a little over 7400 packages and 5300 packages, respectively.

Both AlmaLinux and Rocky Linux provide migration tooling to assist with system conversion from another distribution.

AlmaLinux provides the ELevate tool which supports “migration between major versions of RHEL derivatives" so that users can "easily go from CentOS 7.x to any 8.x”.

Rocky Linux provides the migrate2rocky tool. Rocky’s utility is intended to migrate within a major version, providing different scripts for EL8 to Rocky8 or EL9 to Rocky9 migrations. migrate2rocky minimizes the number of variables it needs to handle during migration by requiring the EL8.x system to be upgraded to at least 8.5. The documentation includes commands to modify the CentOS repos so CentOS systems < 8.5 can upgrade 8.5 prior to migration.
 

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Support and Enterprise Viability

Enterprise viability is strong with both options. Here at OpenLogic, we look at several factors to determine if a distribution is “enterprise ready.” The items that the distribution must provide are:

• A rich package count, including a widely distributed mirror network
• Updates (major and/or minor version OS releases)
• Patching (package updates within a major/minor version)
• Documentation

There are two other items that are necessary. These may not be provided by the distribution themselves but may be provided by one or more 3rd parties:

• Support with an SLA
• Availability of professional services

AlmaLinux and Rocky Linux both provide all the distribution items as well as support from their founding companies.

Checking the last box of this Enterprise Linux checklist, professional services may be available from the founding companies, but 3rd party support and professional services are available. For instance, OpenLogic provides support and professional services for AlmaLinux, Rocky Linux, and several other Enterprise Linux distributions.

Other Notable Differences

Some Linux distributions have been considered not ready for enterprise use simply due to the lack of public mirrors hosting the distro’s packages. If a distribution only has a very small handful of mirrors, the possibility of mirrors being unreachable (or unusably slow) is too high for mission critical systems to rely on them.

Neither AlmaLinux nor Rocky Linux need worry here!

AlmaLinux presently has 395 mirrors announcing support for FTP, HTTP/HTTPS, and RSYNC (with many mirrors supporting IPv6) while Rocky Linux presently has 151 mirrors announcing support for HTTP/HTTPS and RSYNC.

Final Thoughts

While comparing AlmaLinux vs. Rocky Linux it is a worthwhile exercise for teams considering their next Enterprise Linux distro, at the end of the day both distros are very similar. And, given the quality of releases to this point, enterprises can find success with either option.

Additional Resources

• Blog - Applying CIS Benchmarks to Your Linux OS With Hardened Images
• Video - How Rocky Linux and AlmaLinux Keep Their Distributions Secure
• White Paper - Decision Maker's Guide to Enterprise Linux
• Blog - How to Plan a CentOS to AlmaLinux Migration
• Blog - Planning a CentOS to Rocky Linux Migration
• Blog - All About Rocky Linux 9.1
• Blog - What's New in AlmaLinux 9
• Blog - Finding the Best Linux Distro