How to Upgrade from CentOS 7 to AlmaLinux 8 or 9 on Your VPS or Dedicated Server

With CentOS 7 reaching its end of life, upgrading to a modern and supported OS like AlmaLinux 8 or 9 is crucial for continued stability, security, and performance. AlmaLinux offers a seamless and reliable transition path as it’s built to be a 1:1 RHEL binary compatible fork, making it an excellent choice for CentOS users.

Prerequisites

• A VPS or dedicated server running CentOS 7.
• Root access to the server.
• A recent backup of your server’s data and configurations.
• Ensure your system is fully updated.

Step-by-Step Guide to Upgrading from CentOS 7 to AlmaLinux 8/9

Step 1: Update and Prepare Your System

1. Log in to your CentOS 7 server via SSH as the root user or a user with sudo privileges.
2. Update all system packages:

   sudo yum update -y

3. Reboot your server to ensure all updates are applied:

   sudo reboot

4. Verify your CentOS version:

   cat /etc/centos-release

You should see output similar to CentOS Linux release 7.x.x (Core).

Step 2: Install the ELevate Tool

The ELevate tool is used to migrate from CentOS 7 to AlmaLinux 8 or 9.

1. Add the ELevate repository:

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

2. Install the leapp package:

   sudo yum install -y leapp

Step 3: Check for Upgrade Compatibility

1. Run a pre-upgrade check:

   sudo leapp preupgrade

2. Review the pre-upgrade report:
   The report is located at /var/log/leapp/leapp-report.txt. It will detail any issues that need to be resolved before proceeding.
3. Address any issues raised in the report. Common issues may include unsupported packages, custom configurations, or third-party repositories.

Step 4: Begin the Upgrade Process

1. Start the upgrade process:

   sudo leapp upgrade

This process may take some time as it involves downloading and installing new packages, migrating configurations, and updating the kernel.

2. Reboot your server:

   sudo reboot

The system will boot into a special initramfs environment and complete the upgrade.

Step 5: Verify the Upgrade

1. Log back into your server after the upgrade process completes.
2. Check the new OS version:

   cat /etc/redhat-release

You should see output indicating that you are now running AlmaLinux 8 or 9, depending on your chosen target version.

Step 6: Post-Upgrade Tasks

1. Reinstall third-party repositories or packages if necessary.
2. Test critical services and applications to ensure they are functioning correctly.
3. Clean up old packages and files:

   sudo yum autoremove

Troubleshooting Tips

• Check the leapp logs if you encounter issues:
• /var/log/leapp/leapp-upgrade.log
• /var/log/leapp/leapp-report.txt
• Ensure your system has enough free disk space for the upgrade process.
• Disable any custom or third-party repositories that may cause conflicts and re-enable them after verifying compatibility with AlmaLinux.

Conclusion

Upgrading from CentOS 7 to AlmaLinux 8 or 9 ensures continued support, security, and compatibility for your server. With the ELevate tool, the migration process is straightforward, allowing you to maintain your existing setup with minimal downtime and effort.