Oracle Linux

Oracle Linux is an enterprise Linux distribution built by Oracle Corporation from RHEL source code. It is free to download and use, and offers unique technical advantages such as the Unbreakable Enterprise Kernel (UEK) and Ksplice zero-downtime kernel patching.

Overview

Oracle Linux has been available since 2006, making it one of the earliest RHEL-compatible distributions. Unlike community projects such as AlmaLinux and Rocky Linux, Oracle Linux is directly maintained and supported by a major commercial corporation.

Core Positioning

• Free to download, use, and distribute
• Optional commercial support (Oracle Premier Support)
• Optimized for the Oracle technology stack (database, middleware, cloud)
• Unique UEK kernel and Ksplice technology

History

Year	Event
2006	Oracle releases Oracle Enterprise Linux (later renamed Oracle Linux)
2006	Oracle launches “Unbreakable Linux” support program
2012	Oracle acquires Ksplice technology
2013	Oracle Linux 6 introduces UEK R2
2019	Oracle Linux 8 released
2022	Oracle Linux 9 released
2025	Oracle Linux 10 released

Dual Kernel Strategy

Oracle Linux’s most distinctive feature is offering two kernel options.

UEK (Unbreakable Enterprise Kernel)

UEK is an enterprise-grade kernel customized by Oracle based on a newer upstream Linux kernel:

• Based on more recent Linux mainline kernel versions (rather than RHEL’s older kernel with backported patches)
• Optimized for Oracle Database, Oracle Cloud, and modern workloads
• Includes additional performance enhancements and new features
• Installed and enabled by default

Oracle Linux Version	UEK Version	Based on Kernel
OL 8	UEK R6/R7	5.4 / 5.15
OL 9	UEK R7 initially; UEK R8 default for new installs since 9.6	5.15 / 6.12
OL 10	UEK R8	6.12

RHCK (Red Hat Compatible Kernel)

RHCK is the kernel identical to RHEL:

• Binary-compatible with the RHEL kernel
• Suitable for scenarios requiring strict RHEL compatibility
• Can be switched after installation
• x86_64 only; aarch64 ships UEK only (Oracle release notes)
• Existing OL 9 systems upgraded to 9.6+ do not automatically switch to UEK R8 (only new installs default to R8)

# Check current kernel
uname -r

# Switch default kernel to RHCK
sudo grubby --set-default /boot/vmlinuz-$(rpm -q kernel --qf '%{VERSION}-%{RELEASE}.%{ARCH}\n' | tail -1)

# Switch default kernel to UEK
sudo grubby --set-default /boot/vmlinuz-$(rpm -q kernel-uek --qf '%{VERSION}-%{RELEASE}.%{ARCH}\n' | tail -1)

# Reboot to apply changes
sudo reboot

UEK vs RHCK: When to Use Which

Scenario	Recommended Kernel
Oracle Database	UEK
Oracle Cloud	UEK
Need latest kernel features	UEK
Third-party software requires RHEL kernel	RHCK
Need RHEL-certified hardware drivers	RHCK
Mixed RHEL and OL environment	RHCK

Ksplice: Zero-Downtime Kernel Patching

Ksplice is one of Oracle Linux’s most compelling technologies, allowing kernel security patches to be applied without rebooting the system.

How It Works

Ksplice uses runtime binary code replacement to dynamically apply patches while the kernel is running:

• No server restarts required
• No maintenance windows needed
• Security patches can be applied immediately upon release
• Works with both UEK and RHCK

Usage

# Check available Ksplice updates
sudo ksplice show

# View known security updates
sudo ksplice known

# Apply all available patches
sudo uptrack-upgrade -y

# View applied patches
sudo uptrack-show

Ksplice Licensing

• Oracle Linux Premier Support customers: Included in subscription
• Free users: Ksplice for Oracle Linux (also available for Oracle Cloud free-tier users)

Free Usage Policy

Oracle Linux has an important distinction in its business model — it is completely free:

• Free to download: Anyone can download from Oracle’s website
• Free to use: No license required for production environments
• Free updates: All security and feature updates via Oracle’s public yum repositories
• Free to redistribute: Open-source licenses allow free distribution

Commercial support (Oracle Premier Support) is an optional paid service.

Oracle Cloud Integration

Oracle Linux is the native operating system for Oracle Cloud Infrastructure (OCI):

• OCI compute instances provide Oracle Linux images by default
• Deep integration with Oracle Cloud services
• Oracle Autonomous Linux: Automated OS management
• Using Oracle Linux on OCI includes Premier Support

Oracle Autonomous Linux

This is an automated management service for Oracle Linux on OCI:

• Automatic security patching (via Ksplice)
• Automatic compliance checking
• Automatic performance tuning
• Reduced manual operational overhead

Installation and Configuration

Getting Oracle Linux

Download: yum.oracle.com or edelivery.oracle.com

Repository Structure

# View enabled repositories
dnf repolist

# Oracle Linux 9 main repositories:
# ol9_baseos_latest      BaseOS
# ol9_appstream           AppStream
# ol9_UEKR<N>            UEK kernel (N advances with 9.x minors: R7 was ol9_UEKR7, and 9.6+ defaults to UEK R8;
#                        confirm the repo ID with `dnf repolist | grep -i uek` instead of copying R7 from old articles)
# ol9_codeready_builder  Developer tools

Repository	Description
ol9_baseos_latest	Core system packages
ol9_appstream	Applications and runtimes
ol9_UEKR	UEK kernel (R7 was ol9_UEKR7; 9.6+ defaults to UEK R8 — confirm the ID with dnf repolist)
ol9_codeready_builder	Developer tools and libraries
ol9_addons	Additional packages
ol9_developer	Developer tools
ol9_developer_EPEL	Oracle-maintained EPEL mirror

Post-Installation Setup

# Check system version
cat /etc/oracle-release

# Update the system
sudo dnf update -y

# Enable EPEL
sudo dnf install -y oracle-epel-release-el9

# Enable CodeReady Builder
sudo dnf config-manager --set-enabled ol9_codeready_builder

Migration Tool: migrate-to-oracle-linux (formerly centos2ol)

The Oracle Linux ecosystem provides migrate-to-oracle-linux.sh (repository oracle/migrate-to-ol, formerly centos2ol):

# Download the migration script (follow the repository README for the current URL)
curl -O https://raw.githubusercontent.com/oracle/migrate-to-ol/main/migrate-to-oracle-linux.sh

# Run migration
sudo bash migrate-to-oracle-linux.sh

# Optional: Switch to UEK kernel
sudo dnf install -y kernel-uek
sudo reboot

Note: the repository README states the script is a community effort and is not officially supported by Oracle — rehearse on a test machine and take a full backup before production migration. Supported sources: CentOS Linux 7/8 and other supported EL-family systems (including the Amazon Linux 2 → OL 7 exception), per the repository’s current documentation.

Oracle Premier Support

Oracle’s commercial support includes:

Feature	Description
Technical Support	24/7 technical support
Ksplice	Zero-downtime kernel patching
Lifecycle	Up to 10+ years per version with extended support
Certification	Oracle Database and middleware certification
Compliance	Security compliance tools and reporting

Pricing is typically lower than RHEL subscriptions (Oracle intentionally competes with Red Hat in the enterprise support market).

Ideal Use Cases

Oracle Linux is particularly well-suited for:

• Oracle stack users: Running Oracle Database, WebLogic, Oracle E-Business Suite
• Oracle Cloud users: Native preferred OS on OCI
• Zero-downtime patching needs: Ksplice is highly valuable for high-availability environments
• Need newer kernel features: UEK provides more recent capabilities than the RHEL kernel
• Budget-conscious enterprises: Free to use, purchase support as needed

Less Ideal For

• Organizations with concerns about Oracle (vendor lock-in risk)
• Environments requiring 100% RHEL kernel compatibility (unless switching to RHCK)
• Users preferring purely community-driven projects

Summary

Oracle Linux holds a unique position in the EL ecosystem: it provides RHEL compatibility while offering differentiated value through UEK and Ksplice. For Oracle stack users and scenarios requiring zero-downtime patching, Oracle Linux is a highly competitive choice.