🚀 Upgrading from Oracle Linux 8 to Oracle Linux 9: A Comprehensive Guide

📋 Prerequisites

Before initiating the upgrade, ensure the following:

System Version: Confirm you're running Oracle Linux 8.10.

cat /etc/os-release 

Backup: Take a full system backup or create a VM snapshot to safeguard against potential issues.

Secure Boot: Disable Secure Boot if enabled.

sudo mokutil --sb-state

Locale Settings: Ensure the system locale is set to en_US.UTF-8.

sudo localectl set-locale LANG=en_US.UTF-8

SELinux: Temporarily disable SELinux.

sudo setenforce 0
sudo sed -i 's/^SELINUX=.*/SELINUX=permissive/' /etc/selinux/config

Firewall Configuration: Disable AllowZoneDrifting in the firewall configuration.

sudo sed -i 's/^AllowZoneDrifting=.*/AllowZoneDrifting=no/' /etc/firewalld/firewalld.conf

Network Filesystems: Unmount any network-mounted filesystems and comment them out in /etc/fstab.

Proxy Settings: If your system uses a proxy, configure it in /etc/yum.conf.

sudo vim /etc/yum.conf
# Add the following line
proxy=http://proxy-url:port

Disable root login over SSH:

Open the SSH configuration file: 

Use a text editor with root privileges, such as sudo nano /etc/ssh/sshd_config or sudo vi /etc/ssh/sshd_config. 

Locate the PermitRootLogin setting: 

Search for the line containing PermitRootLogin. It might be commented out with a # at the beginning. 

Change the value: 

If the setting is PermitRootLogin yes, change it to PermitRootLogin no. If it's commented out, uncomment it and set it to no. 

Save the changes: 

Save the modified sshd_config file. 

Restart the SSH service: 

Use a command like sudo systemctl restart sshd or sudo service ssh restart.

🔄 Step-by-Step Upgrade Process

1. Update the System

Ensure all packages are up to date.

sudo dnf update -y
sudo reboot

2. Install the Leapp Utility

Install the Leapp upgrade tool and enable necessary repositories.

sudo dnf install -y leapp-upgrade

3. Run Pre-Upgrade Checks

Execute the pre-upgrade process to identify potential issues.

sudo leapp preupgrade --enablerepo 'ol9_baseos_latest' --enablerepo 'ol9_appstream' --enablerepo 'ol9_UEKR7'

Review the generated report:

cat /var/log/leapp/leapp-report.txt

Address any inhibitors or warnings highlighted in the report.

4. Perform the Upgrade

Once all issues are resolved, initiate the upgrade.

sudo leapp upgrade

5. Reboot into the Upgrade Environment

After the upgrade process completes, reboot the system.

sudo reboot

During boot, select the "Leapp Upgrade" entry to proceed with the upgrade to Oracle Linux 9.

✅ Post-Upgrade Steps

After the system boots into Oracle Linux 9:

Verify OS Version:

cat /etc/os-release

Re-enable SELinux:

sudo sed -i 's/^SELINUX=.*/SELINUX=enforcing/' /etc/selinux/config
sudo setenforce 1

Re-enable Services: Start any services that were disabled prior to the upgrade.

Test Applications: Ensure all applications and services function as expected.

🧯 Rollback Strategy

Leapp does not support automatic rollback. It's crucial to have a full system backup or VM snapshot before initiating the upgrade, allowing you to restore the system if necessary.