The recommended in-place upgrade method is to use the Leapp utility. This upgrades the operating system while preserving installed applications and configurations.
For official guidance, see Red Hat's in-place upgrade documentation.
1. Pre-Upgrade Checklist
Before starting:
- Ensure the system is registered with Red Hat Subscription Management.
- Verify you have a valid subscription for both RHEL 8 and RHEL 9 repositories.
- Take a full VM snapshot or backup.
- Confirm the system is running the latest RHEL 8 release.
- Ensure at least 2-4 GB RAM is available
-
Ensure at least 5–10 GB of free space in
/var. - Reboot and verify the system is healthy.
2. Verify Current Version
# cat /etc/redhat-release
Expected output should show RHEL 8.x.
3. Update the System
# dnf clean all
# dnf update -y
# reboot
4. Install Leapp
# dnf install -y leapp-upgrade
For systems using Red Hat repositories, this package is included in standard repositories.
5. Disable Unsupported Repositories
List enabled repositories:
# subscription-manager repos --list-enabled
Disable third-party repositories such as:
- EPEL
- Oracle custom repositories
- Internal repositories not certified for RHEL 9
Example:
# subscription-manager repos --disable=epel
6. Run Pre-Upgrade Assessment
# leapp preupgrade
Review the report:
# less /var/log/leapp/leapp-report.txt
Also review the detailed JSON report:
# less /var/log/leapp/leapp-report.json
7. Resolve Inhibitors
Common issues include:
Deprecated Authentication Modules
For example, removal of pam_pkcs11.
Custom Kernel Modules
Third-party drivers may need updates.
Deprecated Network Scripts
Migrate to NetworkManager.
Removed Packages
Some RHEL 8 packages are no longer available in RHEL 9.
Root SSH Login Settings
Leapp may flag certain SSH configurations.
8. Start the Upgrade
# leapp upgrade
This downloads required RHEL 9 packages and prepares the system.
9. Reboot to Begin Upgrade
# reboot
During boot, the system automatically enters the upgrade environment and performs the upgrade. This can take 15–60 minutes depending on system size and performance.
10. Verify the Upgrade
After the system reboots:
# cat /etc/redhat-release
# uname -r
Expected output:
Red Hat Enterprise Linux release 9.x
11. Validate Applications and Services
Check service status:
# systemctl --failed
Review logs:
# journalctl -p err -b
Confirm critical applications start correctly.
12. Remove Old Kernels and Cleanup
# dnf autoremove -y
# dnf clean all
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