How to Seamlessly Migrate from CentOS to Oracle Linux with Minimal Downtime

Forget piecemeal patches and risky migrations. Discover a step-by-step method to transition your infrastructure from CentOS to Oracle Linux that prioritizes uptime and system integrity—because downtime isn't an option.

In the wake of CentOS shifting its focus away from traditional long-term stable releases, many organizations find themselves at a crossroads. For businesses relying on the dependable stability of CentOS, Oracle Linux emerges as a compelling alternative, offering enterprise-grade support and compatibility without the costly licensing fees of some other distributions.

However, migrating from CentOS to Oracle Linux comes with its own set of challenges: concerns about downtime, application compatibility, and ensuring data integrity throughout the process. In this post, I’ll walk you through a practical, clear path to migrate your systems with minimal disruption — even on live production servers.

Why Migrate from CentOS to Oracle Linux?

Before we jump into the how-to, here's a quick refresher on why this migration matters.

• CentOS Shift: Since December 2020, CentOS Stream replaced CentOS Linux as the upstream source for RHEL (Red Hat Enterprise Linux) updates. This turnaround means less predictability for businesses relying on stable point releases.
• Oracle Linux Advantage: Oracle Linux maintains full binary compatibility with RHEL but also offers free access to support services (optional). It’s battle-tested in enterprise environments and integrates easily with existing RHEL-based workloads.
• Minimal Changes Needed: Oracle Linux maintains high compatibility with your current software stack configured for CentOS.

Preparation: What You Need Before Migrating

1. Backup Everything: Always take full backups of your servers prior to migration! LVM snapshots or rsync backups can safeguard data.

2. Access and Privileges: Ensure you have root or sudo access.

3. Check Repositories: Identify custom repositories and package sources; these might need adjustment post-migration.

4. Test Environment: If possible, replicate a staging environment mimicking your production stack for dry runs.

5. Update System: On your current CentOS machine:

   sudo yum update -y
   sudo reboot
   

Step-by-Step Migration Guide

Step 1: Identify Your Current System Version

Validate the existing OS version:

cat /etc/centos-release

You should see something like:

CentOS Linux release 7.9.2009 (Core)

This helps ensure you're targeting the correct replacement packages.

Step 2: Replace CentOS Repositories with Oracle Linux Repositories

Oracle provides an official oracle-linux-release-el7 package that configures repositories. But first, clean up existing repo files:

sudo rm -f /etc/yum.repos.d/CentOS-*.repo
sudo rm -f /etc/yum.repos.d/epel.repo # if you use EPEL and want fresh EPEL repos later

Download and install Oracle’s release package:

sudo yum install -y https://yum.oracle.com/repo/OracleLinux/OL7/latest/x86_64/getPackage/oraclelinux-release-el7-1.0-14.el7.x86_64.rpm

If using OL8 or OL9, make sure to adjust URLs accordingly (Oracle Yum Server).

Once installed, verify that repo files appear under /etc/yum.repos.d/.

Step 3: Remove Potential Package Conflicts

Sometimes packages installed specifically for CentOS clash with their Oracle equivalents or cause dependency issues.

An optional cleaning step:

sudo yum clean all
sudo rpm -e --nodeps centos-release

Be cautious with removals; running rpm -qa | grep centos can show packages specific to CentOS you might need to handle manually.

Step 4: Synchronize Packages with Oracle Linux Packages

Perform a minimal distro synchronization by upgrading all packages using Oracle repos:

sudo yum distro-sync -y

This command replaces installed packages with their counterparts from Oracle Linux repos while honoring versions and dependencies.

You can check after sync by checking OS release again:

cat /etc/os-release

Expected output would mention Oracle Linux like:

NAME="Oracle Linux Server"
VERSION="7.9"
ID="ol"
ID_LIKE="rhel fedora"
...

Step 5: Rebuild GRUB Bootloader (If Needed)

In most cases GRUB remains functional post-migration but confirm bootloader settings especially if kernel versions change.

sudo grub2-mkconfig -o /boot/grub2/grub.cfg

On UEFI systems:

sudo grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

Step 6: Verify Services and Kernel Version

Check kernel version to confirm you are booting into Oracle's kernel:

uname -r

Oracle's kernels usually include uek (Unbreakable Enterprise Kernel).

Check critical services status (web servers, databases...) just like before migration — no changes expected unless specific kernel modules or drivers are impacted.

Optional: Using oracle-linux-deploy Script for Automated Migration (Oracle 7 only)

Oracle provides an official script simplifying migration — the oracle-linux-deploy.sh script which automates repo swaps and package upgrades during live migrations.

You can fetch it via curl or wget:

curl -O https://yum.oracle.com/oracle-linux-deploy.sh && sudo bash oracle-linux-deploy.sh

Review what it will do before running it in production environments.

Minimizing Downtime Tips

• Use Rolling Updates: Perform migration on one node at a time in clustered environments using load balancers.
• Schedule Maintenance Windows: Notify users beforehand.
• Snapshot VMs: Take VM snapshots before upgrade if applicable.
• Have Rollback Plan Ready: Keep original backups handy in case of emergencies.

By carefully following these procedures during off-peak hours or using cluster rolling updates, you can keep downtime near zero.

Post-Migration: Final Checks & Optional Support Setup

1. Check that all services are operating normally.

2. Confirm that security settings (firewalls, SELinux) remain intact.

3. Review /etc/yum.repos.d/ for any leftover CentOS repo files — remove them.

4. If you want official support from Oracle:

   sudo yum install oraclelinux-release-el7 oracle-olcne-release-el7 oracle-support-release-el7 -y
   

5. Register your system with Oracle Unbreakable Linux Network (ULN) if eligible.

Example Real-Life Scenario — Migrating a Web Server

Suppose this server runs Apache on CentOS 7.

Perform backup:

sudo tar czvf /root/httpd-backup.tar.gz /etc/httpd /var/www/html

Follow migration steps above carefully…

Post-migration verify Apache status:

sudo systemctl restart httpd
sudo systemctl status httpd
curl http://localhost/

If pages load successfully without issues — migration was seamless!

Conclusion

Migrating from CentOS to Oracle Linux is achievable without painful downtime by methodically replacing repository configurations and syncing packages properly. Combined with careful preparation and testing, this approach safeguards uptime while future-proofing your infrastructure onto a supported and enterprise-ready platform.

If you found this guide helpful, consider sharing it with others navigating this transition—and feel free to leave questions below! Together we can make migrations painless for every sysadmin out there.

Happy migrating!
— Your trusted sysadmin blogger