Decorative image for blog on migration from CentOS to AlmaLinux
March 31, 2025

How to Plan a CentOS to AlmaLinux Migration

Operating Systems

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The end of the CentOS Linux community support lifecycle has left many organizations searching for a stable, permanent replacement for their operating systems. AlmaLinux, as an open source RHEL fork, has gained massive traction, especially among system administrators, developers, and IT decision-makers.

However, moving from CentOS to AlmaLinux, particularly in large scale deployments with thousands (or tens of thousands) of servers, is far from a plug-and-play migration. It requires careful planning, technical expertise, and meticulous execution to ensure business continuity and operational efficiency.

Below, we’ll walk you through the essential steps for a successful CentOS to AlmaLinux migration, focusing on some of the common obstacles teams may encounter during the process.

Editor's Note: This blog was originally published on September 12, 2022 and was updated for accuracy in March 2025. 

Table of Contents

  1. Why Migrate From CentOS to AlmaLinux?
  2. CentOS to AlmaLinux Migration Steps
  3. Other Considerations
  4. Final Thoughts
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Why Migrate From CentOS to AlmaLinux?

Red Hat's decision to  phase out CentOS’s stable release model to focus on CentOS Stream — which delivers more frequent updates due to its rolling release model — left enterprises craving stability and predictability. AlmaLinux emerged as one of the top CentOS alternatives due to its binary compatibility with RHEL and its steadfast support of the stable release model.

What Makes AlmaLinux a Good CentOS Alternative?

  • Stability: Unlike CentOS Stream, AlmaLinux stays committed to stability, making it suitable for production environments.
  • Community-Driven: Maintained by the AlmaLinux Foundation, AlmaLinux has an active and devoted community.
  • Binary Compatibility: AlmaLinux mirrors RHEL, ensuring minimal disruptions when transitioning.
  • Cost-Effective: Unlike RHEL, it is free but offers comparable enterprise-level reliability.

If maintaining critical business operations on a predictable, secure Linux distribution is your priority, AlmaLinux is an excellent choice.

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CentOS to AlmaLinux Migration Steps

Migrating hundreds or thousands of systems across environments involves more than swapping repositories. Here we break down the steps involved before, during, and after you migrate. 

1. System and Application Compatibility

Conduct a detailed inventory of your CentOS systems. Identify:

  • Applications, databases, and processes tied to your OS.
  • Third-party packages and dependencies for compatibility checks.
  • Proprietary or custom-built tools that may have version-specific constraints.

2. Hardware Requirements

Ensure your infrastructure supports AlmaLinux versions. Legacy hardware used with CentOS 6 or 7 may need replacements due to incompatibilities with newer kernels.

3. Backup and Rollback Strategies

Before initiating migration, confirm backup systems are in place and test their validity:

  • Perform full system snapshots and data backups.
  • Ensure rollback plans can reinstate current setups in case the transition introduces issues.

4. Testing and Validation

Pilot migrations in a staging environment, simulating production operations. Address migration errors or failures before implementing across critical systems.

5. Choosing the Right Migration Path

Select between in-place migration or new environment deployment. Each approach has distinct tradeoffs:

  • In-place migrations: Best for physical hardware when no substantial downtime is allowed. However, it carries risks of disruptions if interrupted.
  • New environment deployments: Ideal for virtualized or cloud systems. This approach minimizes disruptions but requires additional hardware or temporary instances.

If you are on physical hardware, migrating in place may be the easiest (and cheapest) route because it does not require more systems. In this scenario, it’s important to make sure that connections are stable, and the machine will be available the whole time, because the system could end up in an unrecoverable state if the script gets interrupted. If that were to happen, you would need a rescue disk and some manual work to get back to functionality. If you can't take a system out of use to rebuild, then running the migration may be the best option.

However, if you have spare hardware or are on a virtualized infrastructure, it would be preferable (and safer) to build a new system to your specifications, migrate the apps and data over, and then replace the old system with the new one.

Carefully weigh these considerations to tailor your CentOS migration strategy for your unique needs. Now let's look at some actual migration paths:

CentOS 6 to AlmaLinux Migration Path

Since there is no direct migration path from Centos 6 to AlmaLinux (AlmaLinux starts at 8.4), you must be on CentOS 8.4 at least in order to migrate.

Two possible approaches — the first would be to upgrade from 6 to 7 to 8, and then migrate your data. However, this would be time-consuming and risky because of all the package changes between major versions.

The second (and more advisable) approach is to build a new machine prior to migrating. Best case scenario: All required third-party software has a new version, and data can be safely upgraded. Worst case: There is software that depends on CentOS libraries. If the latter is true, you would need to either find alternatives, or identify a way to run the software anyway. Fortunately, containerization makes it relatively easy nowadays to run older versions of software on newer systems, or even on completely different distributions.

CentOS 7 to AlmaLinux Migration Path

The migration path for CentOS 7 is virtually identical to CentOS 6, but a little easier because CentOS 7 already uses systemd for service management, whereas CentOS 6 uses legacy SysV init scripts. There are a few other changes, but that is a major one that makes upgrading from 7 less complex than 6.

For detailed instructions on how to migrate from CentOS 7 to AlmaLinux 9 (the current version), take a look at this blog on CentOS to Rocky Linux migration and simply ignore the steps that are specific to converting from the latest version of Alma to the latest version of Rocky. 

CentOS 8 to AlmaLinux Migration Path

Since CentOS 8 and AlmaLinux 8 are nearly identical, this is a relatively painless migration. Minor changes only; the CentOS repos are swapped out for AlmaLinux repos, and a handful of packages (mostly branding packages) are replaced.

CentOS Stream to AlmaLinux Migration 

The almalinux-deploy.sh script automates the process of converting a CentOS Stream system to AlmaLinux 8. It creates the repo files for AlmaLinux, replaces branded packages, and then performs a distro-sync to sync up the system to the current version of the packages in the repos.

Note: The migration will work with CentOS Stream, but some packages may be a little newer than the current AlmaLinux packages, so it downgrades packages using distro-sync to match the current version in the repos.

6. Run Pilot Migrations

Select non-critical systems to test the migration process:

  • Execute the switch to AlmaLinux.
  • Validate applications and services post-migration.
  • Modify or replace failed dependencies.

Based on test results, refine the migration plan for production systems.

7. Full-Scale Deployment

Once confident, proceed with rolling out migrations across production systems:

  • Schedule migrations during downtime or maintenance windows.
  • Maintain dedicated technical teams ready to handle interruptions on the fly.

Implement migrations in phases to minimize potential disruptions and rollback issues.

8. Post-Migration Testing

Run complete QA procedures post-migration:

  • Verify application functionality and security.
  • Monitor system logs for errors or warnings.
  • Confirm user access and permissions are intact.

Fix issues before declaring the migration successful.

9. Ongoing Maintenance

Post-migration upkeep ensures systems remain secure and scalable:

  • Enable AlmaLinux repos for regular OS updates.
  • Schedule periodic system health checks.
  • Establish monitoring and alert systems for performance optimization.
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Other Considerations

The only official migration script is almalinux-deploy.sh, provided by AlmaLinux itself. This script will not only migrate CentOS 8 to AlmaLinux, but also Oracle Linux 8, RHEL 8, Rocky Linux 8, Virtuozzo Linux (VZLinux) 8, and CentOS Stream, along with the version 9 variants. There may be others out there, but you should proceed with caution, and verify the script does what is wanted.

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Final Thoughts

Executing a CentOS to AlmaLinux migration is not without its challenges, but with proper planning and resource allocation, your organization can smoothly transition to a stable and future-proof Linux distribution. While migration may feel daunting, following structured processes ensures minimal risk while maximizing uptime for your business.

Lastly, if you’re navigating a large-scale migration and lack internal expertise, OpenLogic’s Linux experts can alleviate the strain. We can offer guidance or our Professional Services team can perform the migration itself. Once you have successfully migrated, we also offer 24/7 AlmaLinux support. 

This Blog Was Written by an OpenLogic Linux Expert

For unparalleled expertise with all flavors of Enterprise Linux, partner with OpenLogic. We can provide technical support as well as professional services including migrations, consultations, and training. 

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Lance Dillion Bio

Lance Dillon

Enterprise Architect

Lance has been working in the IT field for over 30 years, most of it concentrated on data centers and infrastructure. For the past 10 years he has focused on SaaS infrastructure, ensuring reliability, high availability, and scalability of systems. He has been working with CentOS and Linux distributions for the past 25 years.