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Oracle Linux (OL), formerly known as Oracle Enterprise Linux or OEL), is a Linux distribution packaged and freely distributed by Oracle, available partially under the GNU General Public License since late 2006. It is compiled from Red Hat Enterprise Linux (RHEL) source code, replacing Red Hat branding with Oracle's. It is also used by Oracle Cloud and Oracle Engineered Systems such as Oracle Exadata and others.

Oracle Corporation distributes Oracle Linux with two alternative Linux kernels:

• Red Hat Compatible Kernel (RHCK) – identical to the kernel shipped in RHEL
• Unbreakable Enterprise Kernel (UEK[7]) – based on newer mainline Linux kernel versions, with Oracle's own enhancements for OLTP, InfiniBand, SSD disk access, NUMA-optimizations, Reliable Datagram Sockets (RDS), async I/O, OCFS2, and networking.

Oracle promotes Unbreakable Enterprise Kernel as having 100% compatibility with RHEL, even though this is essentially impossible to guarantee due to the kernel's ABI changing due to various factors, including the kernel being based on a newer version which has many thousands of differences from Red Hat's kernel. While the Linux kernel developers, upstream, try never to break userspace, it has happened before. Oracle's compatibility claims lead the user to conclude that third-party RHEL-certified applications will behave properly on the Oracle kernel, but it does not provide any reference to third-party documentation.

Source: https://en.wikipedia.org/wiki/Oracle_Linux