Consolidation as an industry trend - Expert Consolidation in Oracle Database 12c - page 22

strength, the same cannot be said about SuSE. Nevertheless their distributions are both widely spread, with Red Hat
Enterprise Linux 6 and SuSE 11 being the current distributions. Another noteworthy distribution for Oracle, Asianux,
is less widely spread in the English-speaking world but focuses on Asia, as the name implies.
Thanks to the copyleft clause in most free software, any distribution has to distribute the source code as well. This
allows “clones” of popular distributions to appear. For an Oracle administrator, distributions based on the Red Hat
Package Manager (RPM) are most relevant since only these are supported. Of all these, Red Hat is probably the most
important one due to its market share. There are a number of clones for Red Hat: Scientific Linux and CentOS are the
most popular. A more recent Red Hat derivative is Oracle Linux, which started off as a near identical clone without
the copyrighted material such as logos. Additionally, Oracle has developed its own kernel which is shipped in parallel
with the Red Hat kernel, while otherwise maintaining capability with Red Hat.
The non RPM-based distributions like Debian, Ubuntu, and their derivatives may have wider adoption, especially
on the netbook and laptop class of hardware than Red Hat clones. However, they do not play a role for Oracle database
deployments.
Despite the initial skepticism and aggressive marketing efforts trying to diminish its importance Linux is
powering lots of business-critical applications and managed to get into even the most conservative industries. It has
more than challenged traditional UNIX variants, for two main reasons: it compares to them in terms of scalability
and stability, but it can also be deployed on industry standard hardware, significantly lowering the cost of entry for
businesses.
The Linux Kernel
The Linux kernel alongside the C-library and compilers (and of course other tools) forms the core of the Linux
system. It has been continuously developed, and at quite a rapid pace. The kernel release cycles adhere to the open
source motto: test and release often! Thanks to the efforts of so many individuals, the kernel runs on more hardware
platforms than any other system in the world. This is very remarkable, especially since Linus Torvalds didn't envisage
portability of his code outside the 80386 processor world.
What is confusing to many new Linux users is the naming of the kernel, and the difference between the mainline
kernel and the kernel used in Red Hat, SuSE Linux and Oracle Linux. For a long time, the kernel development was
divided into a stable and development tree. For example, kernel 2.4.x represented the stable tree while the
kernel-in-development version was 2.5. This led to the problem that 2.5 was considered unstable, yet it provided
support for current hardware. Users of kernel 2.4 lagged significantly behind the unstable tree. When kernel 2.6 was
introduced the development model changed, and there was no more odd/even branch.
The confusion starts when comparing the mainline kernel developed by Linus Torvalds and the other
kernel maintainers with the one used in the distributions. Red Hat 6.x for example used a kernel named 2.6.32.x.
Kernel-2.6.32 dates back to December 2009 according to the kernel.org website. What you need to know is that the
actual kernel shipped with the distribution but is merely based on 2.6.32.x. It includes many patches that have been
added into it. Most of these patches are taken from upstream development, either to add features or bug fixes, or to
add support for hardware that was not yet available when the base kernel was released. So when dealing with the Red
Hat kernel, bear in mind that it is not necessarily the version you think it is.
The Unbreakable Enterprise Kernel or Kernel-UEK
When Oracle announced Enterprise Linux it was a nearly identical clone of Red Hat's Enterprise Linux with only a
few exceptions that did not impact the way the system operated. This was only the first step though, and after a little
while when RHEL 6 was still in development, Oracle introduced their Enterprise Kernel to the user community. Like
Red Hat's kernel it was based on 2.6.32, but it could be used for Oracle Linux/Red Hat Enterprise Linux 5. As a sign of
confidence, the Unbreakable Kernel is installed by default starting with Enterprise Linux 5.6. The Red Hat compatible
kernel is still shipped, and is installed in parallel but is not selected as the default in the boot loader.