How to Migrate from CentOS 7 to AlmaLinux 8 and AlmaLinux 9: A Step‑by‑Step Guide

CentOS 7 will stop receiving security updates after June 30 2024, leaving servers vulnerable. The official CentOS Stream is a testing branch and not suitable for production, so staying on CentOS 7 is equivalent to running an unpatched system.

Why you must abandon CentOS

CentOS 8 was retired at the end of 2021, and CentOS 7 is the last long‑term support release that is now discontinued. The recommended replacement, CentOS Stream, is unstable for enterprise use. In short: not migrating means running without security patches.

Preparation before migration (three essential tasks)

1. Backup everything – back up system configuration ( /etc ), user data ( /home ), installed package list ( sudo rpm -qa > installed_packages.txt ), and databases (MySQL, PostgreSQL, etc.). A simple tar command can pack the key directories:

sudo tar -czvf backup.tar.gz /etc /home /var/lib/mysql

2. Check hardware and software compatibility – ensure at least 20 GB of free disk space and verify that packages installed on CentOS 7 are compatible with AlmaLinux 8/9.

3. Temporarily disable security services – turn off SELinux and the firewall to avoid interruptions during the upgrade:

sudo setenforce 0          # temporarily disable SELinux
sudo systemctl stop firewalld  # stop firewall

Migration Phase 1: CentOS 7 → AlmaLinux 8

Step 1: Update the current system

sudo yum clean all
sudo yum update -y
sudo reboot

Step 2: Install the migration tool “Leapp” (Elevate)

sudo yum install -y http://repo.almalinux.org/elevate/elevate-release-latest-el7.noarch.rpm

Step 3: Pre‑upgrade check

sudo leapp pre-upgrade   # scans for potential issues

Address any reported problems, such as multiple kernels (remove extras with sudo rpm -e ) or old driver conflicts.

Step 4: Perform the upgrade

sudo leapp upgrade   # starts the migration, will reboot twice automatically

Step 5: Verify the upgrade

cat /etc/os-release   # should show AlmaLinux 8

Clean residual CentOS packages and caches:

sudo yum clean all
sudo rm -rf /var/cache/yum

Migration Phase 2: AlmaLinux 8 → AlmaLinux 9

Step 1: Update AlmaLinux 8

sudo dnf clean all
sudo dnf update -y
sudo reboot

Step 2: Install the ELevate tool (still required)

sudo dnf install -y alinux-elevate-release
sudo dnf install -y elevate-upgrade

Step 3: Pre‑check and upgrade

sudo elevate-upgrade pre-upgrade   # checks for issues
sudo elevate-upgrade upgrade       # performs the upgrade

Again, the system will reboot automatically.

Step 4: Post‑upgrade cleanup

sudo dnf clean all
sudo systemctl enable --now firewalld   # re‑enable firewall
sudo setenforce 1                      # re‑enable SELinux

After migration – five essential tasks

Check service status: systemctl list-units --type=service

Update software repositories – replace old CentOS repos with AlmaLinux repos.

Re‑compile or reinstall kernel modules (e.g., NVIDIA drivers) if needed.

Restore backed‑up data: tar -xzvf backup.tar.gz -C /

Monitor system logs for errors: journalctl -xe

Common pitfalls

Power or network loss during migration – always use a wired connection and UPS.

Leaving multiple old kernels installed – keep only one and remove the rest with sudo rpm -e .

Forgetting to disable SELinux – see the commands in the preparation section.

Software incompatibility after upgrade – downgrade problematic packages with dnf downgrade or contact the vendor.

Final reminder

If this is your first migration, practice on a virtual machine (VirtualBox or VMware) before touching production servers. AlmaLinux offers long‑term support and a vibrant community, making it a stable foundation for future workloads.