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Seamless Migration: A Step-by-Step Guide to Upgrading from CentOS 7 to AlmaLinux

Forget the panic around CentOS 8's shift; the real challenge is mastering a smooth, zero-downtime migration on your existing CentOS 7 servers to AlmaLinux — an underappreciated, enterprise-ready fork that deserves a spot in your upgrade strategy.

With CentOS 7 approaching its end of life (EOL), organizations still relying on these servers face inevitable decisions: do you stick with outdated software and risk security and stability issues, or do you migrate? AlmaLinux presents itself as a rock-solid, free, and community-supported alternative designed for enterprise environments. It’s binary-compatible with RHEL (Red Hat Enterprise Linux), making it an ideal drop-in replacement for CentOS.

In this guide, I’ll walk you through a step-by-step migration from CentOS 7 to AlmaLinux, focusing on practical tips that keep your systems running smoothly—without expensive downtime or costly re-installations.

Why Upgrade from CentOS 7 to AlmaLinux?

• CentOS 7 EOL: Official support and updates end in June 2024.
• Security & Stability: AlmaLinux continues full security patches and system updates aligned with RHEL.
• Enterprise-ready: Tested for scalability and production workloads.
• Zero licensing costs: Like CentOS was originally designed.
• Community-driven with commercial support options.

Preparing for Your Migration

Before diving into the process, preparation is key to avoiding surprises:

1. Backup Everything

Make backups of critical data & configuration:

# Backup important directories (example)
tar czvf /backup/etc-backup.tar.gz /etc
tar czvf /backup/var-backup.tar.gz /var
# Dump databases if applicable
mysqldump -u root -p --all-databases > /backup/all_databases.sql

Use your preferred tools like rsync, or snapshots if using virtual machines.

2. Check Your Current OS Version and Packages

cat /etc/centos-release
rpm -qa --qf "%{NAME}-%{VERSION}-%{RELEASE}\n" > installed-packages.txt

Keep this list handy for reference.

3. Disable Third-party Repositories

Third-party repos might cause conflicts during migration:

sudo yum-config-manager --disable epel*
sudo yum-config-manager --disable remi*

You can re-enable later after migration if needed.

Step 1: Install the AlmaLinux Migration Tool

The AlmaLinux team provides an official tool called almalinux-deploy which automates much of the heavy lifting.

Add the AlmaLinux Repository & Install Script

curl -O https://raw.githubusercontent.com/AlmaLinux/almalinux-deploy/master/almalinux-deploy.sh
chmod +x almalinux-deploy.sh

Step 2: Run the Migration Script

Before proceeding, read output carefully since this will replace base system RPMs.

sudo bash almalinux-deploy.sh

What happens here?

• The script replaces centos-release RPM with almalinux-release.
• It swaps out branding.
• Adjusts yum repos for AlmaLinux mirrors.
• Updates essential system packages inline without requiring a fresh install.

Step 3: Verify the Operating System Change

Reboot after migration completes:

sudo reboot

Once back up:

cat /etc/os-release

Expected output snippet:

NAME="AlmaLinux"
VERSION="8.x"
ID="almalinux"
...

(Note: For CentOS 7 to AlmaLinux migration, ensure you are aware that official tools mostly target migrating CentOS 8.x to AlmaLinux 8.x. For CentOS 7 compatibility with AlmaLinux 8.x specifically, testing is critical because it's not an in-place upgrade across different major versions.)

Important Considerations with CentOS 7 → AlmaLinux

CentOS 7 is based on RHEL 7 and differs significantly from RHEL/AlmaLinux 8 which is lifted heavily toward newer systemd versions & tech stack changes.

If your goal is strictly migrating CentOS 7 (RHEL7) to AlmaLinux 8, no fully automated tool exists yet for safe in-place upgrade given the kernel and core system differences — it’s effectively a major OS upgrade, not just a rebranding switch.

Recommended Approach for CentOS 7 Users:

1. Fresh Install of AlmaLinux 8

   Build new machines or containers with AlmaLinux 8 fresh installation matching your current server roles as closely as possible.

2. Data Migration

   Carefully migrate data/configuration files using rsync and reinstall needed services on new machines.

3. Test Rigorously

   Validate workloads behavior before switching production workloads over.

4. Switch Over DNS/IP

   When ready, switch over traffic once confident stability is confirmed.

Example: Migrating an Apache Server Config

On old CentOS7 server:

rsync -avz /etc/httpd/conf/ user@new-almalinux-server:/etc/httpd/
rsync -avz /var/www/html/ user@new-almalinux-server:/var/www/html/

Install Apache on AlmaLinux:

sudo dnf install httpd -y
sudo systemctl enable httpd --now

Review configs as some directives may differ due to version changes; test websites thoroughly before final cutover.

Summary Checklist for Smooth Migration From CentOS 7 to AlmaLinux

Final Thoughts

While there might be some panic surrounding past shifts like the surprise end of CentOS Linux as we knew it with version 8, the most critical challenge right now is how you handle legacy systems on CentOS 7 costs-effectively and reliably.

Taking measured steps—especially performing fresh installs and migrating workloads carefully—is advisable until automated smooth in-place upgrades become fully mature tools for major version jumps like RHEL/CentOS7 → AlmaLinux8 migrations.

AlmaLinux shines as a future-proof enterprise-grade OS that can keep your infrastructure secure, stable, and scalable well beyond the sunset of CentOS releases — making it a smart choice for any organization ready for next-gen Linux deployments.

Good luck with your migration journey! If you faced challenges along the way or have tips to share about upgrading from CentOS versions, feel free to drop comments below!

Happy migrating!

If you'd like me to create instructions focused more on any specific scenario — say containerized environments, database servers, or automation scripts — just let me know!