Upgrade from RHEL 6 to RHEL 8: Steps & Risks

To upgrade from RHEL 6, you must move to RHEL 8 (or RHEL 9) because Red Hat ended support for RHEL 6 and there is no direct in-place upgrade path. This article explains the supported upgrade routes, the risks involved, and the exact steps to migrate your system successfully.

Why RHEL 6 Cannot Be Upgraded Directly

Red Hat Enterprise Linux 6 reached End of Maintenance Support on November 30, 2020, and End of Extended Life Phase 1 on June 30, 2024. After these dates, no new security patches, bug fixes, or hardware enablement are provided unless you purchase an Extended Life Cycle Support (ELS) add-on. More importantly, the upgrade tooling in RHEL 6 (the preupg assistant and the Red Hat Upgrade Tool) was designed to move systems to RHEL 7, not to RHEL 8. RHEL 8 introduced a new in-place upgrade path using the Leapp utility, but Leapp only supports upgrades from RHEL 7. Therefore, a direct upgrade from RHEL 6 to RHEL 8 is not supported by Red Hat.

Supported Upgrade Paths from RHEL 6

Red Hat officially supports two routes to reach RHEL 8 from RHEL 6:

• Two-step in-place upgrade: First upgrade RHEL 6 to RHEL 7 using the old Red Hat Upgrade Tool, then upgrade RHEL 7 to RHEL 8 using Leapp. This is the only in-place method that avoids reinstalling the OS.
• Fresh installation: Install RHEL 8 from scratch on new or repurposed hardware, then migrate your applications and data. This is the cleanest and often the most reliable approach, especially if your hardware is older than RHEL 8 supports.

Some third-party tools claim to perform a direct RHEL 6-to-8 migration by converting the system to a different distribution first, but these are not supported by Red Hat and may violate your subscription agreement.

Pre-Upgrade Assessment: What to Check Before Moving

Before attempting any upgrade, you must audit your system. Red Hat provides the preupg assistant for RHEL 6-to-7 upgrades and the leapp preupgrade command for RHEL 7-to-8. Both tools scan your system and produce a report of potential blockers. Key things to check:

• Hardware compatibility: RHEL 8 requires a 64-bit x86 processor, at least 1 GB RAM (2 GB recommended), and 20 GB disk space. Your CPU must support the x86-64-v2 microarchitecture level (roughly any Intel or AMD CPU from 2009 onward).
• Software repositories: Ensure you have valid RHEL 6 and RHEL 7 subscriptions. The upgrade tools need access to the respective repos.
• Custom packages: Any third-party RPMs must have RHEL 8 versions. Use rpm -qa to list installed packages and cross-check each one.
• Kernel modules: Out-of-tree drivers (e.g., proprietary graphics, storage controllers) must be recompiled for the RHEL 8 kernel.
• Services and configs: Systemd replaces SysVinit in RHEL 7 and 8. Service names and configuration files may change (e.g., network becomes NetworkManager).

Step-by-Step: Two-Step In-Place Upgrade

This is the only Red Hat-supported in-place path. It involves two full upgrades, each requiring a reboot. Plan for several hours of downtime and always take a full backup first.

1. Back up everything: Use dump, tar, or a disk image tool. Store the backup off-box.
2. Upgrade RHEL 6 to RHEL 7:
   • Install the Red Hat Upgrade Tool: yum install redhat-upgrade-tool.
   • Run preupg to assess readiness and review the report.
   • Run redhat-upgrade-tool --network 7.9 --instrepo (replacing with your repo URL).
   • Reboot when prompted. The system will boot into RHEL 7.
3. Upgrade RHEL 7 to RHEL 8:
   • Install Leapp: yum install leapp.
   • Run leapp preupgrade and fix all reported inhibitors.
   • Run leapp upgrade.
   • Reboot. The system will boot into RHEL 8.
4. Post-upgrade tasks: Verify services, update configuration files, and run subscription-manager attach to ensure your RHEL 8 subscription is active.

Common Problems and How to Avoid Them

Most upgrade failures come from a few predictable issues:

• Missing or disabled repositories: The upgrade tools need the base, optional, and extras repos. Ensure they are enabled and reachable.
• Custom kernel modules: If you have a module not in the standard kernel, it will block the upgrade. Remove or update it before starting.
• Insufficient disk space: Each upgrade step needs about 5-10 GB free. Check with df -h.
• Firewall and SELinux: Leapp may disable SELinux if it detects a misconfiguration. Re-enable it after the upgrade and restore the correct context.
• Application compatibility: Python 2 is gone in RHEL 8; any scripts using it must be rewritten for Python 3. Also, MySQL is replaced by MariaDB, and PHP versions differ.

Costs and Time Considerations

Upgrading RHEL 6 to RHEL 8 is not free. You need valid subscriptions for RHEL 7 and RHEL 8 (unless you use a free developer subscription). The two-step process can take 4-8 hours of hands-on time, plus testing. If your hardware is older than 10 years, a fresh install may be faster and more reliable. Also, consider that RHEL 8 itself will reach End of Maintenance Support in May 2029, so plan your next upgrade cycle accordingly.

Alternative: Fresh Installation vs. In-Place Upgrade

In-place upgrades preserve your installed packages and configurations, but they can carry forward cruft and misconfigurations. A fresh installation gives you a clean system, but you must reinstall all applications and migrate data. For most production servers, Red Hat recommends a fresh install unless you have a strong reason to preserve the exact system state. The two-step in-place upgrade is riskier because any error in the first step can leave the system unbootable. Always test the upgrade on a clone of your production system first.

Frequently Asked Questions

Can I skip RHEL 7 and go directly from RHEL 6 to RHEL 8?

No. Red Hat does not support a direct in-place upgrade from RHEL 6 to RHEL 8. You must either do the two-step upgrade (6→7→8) or perform a fresh installation of RHEL 8.

What happens if I stay on RHEL 6 after support ends?

You will no longer receive security patches, bug fixes, or hardware enablement. Your system becomes vulnerable to known exploits. You can purchase ELS for up to 4 years, but it is expensive and does not provide new features.

Will my applications run on RHEL 8?

Most applications that run on RHEL 6 will run on RHEL 8, but you may need to update libraries, recompile code, or adjust configuration files. Check each application’s vendor for RHEL 8 support.

How long does the upgrade take?

A typical two-step in-place upgrade takes 4-8 hours, including downloads, package installation, and reboots. A fresh install can be done in 1-2 hours, plus time to reinstall applications and migrate data.

Is it possible to upgrade from RHEL 6 to RHEL 9?

Yes, but only via a fresh installation or a multi-step upgrade: 6→7→8→9. There is no direct path, and each step must be completed before starting the next.

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