Red Hat announced Wednesday the release of Red Hat Enterprise Linux 5.4, a new major point update of the company's popular commercial Linux distribution. This version introduces official support for KVM and marks an important milestone in Red Hat's gradual transition away from Xen.

KVM, the Kernel-based Virtual Machine, is an open source framework that brings native full virtualization to the Linux kernel. It is primarily designed for the x86 architecture (though others are supported) and takes advantage of processor virtualization extensions. It has been part of the mainline Linux kernel since 2.6.20 and has become the favored virtualization solution of the upstream kernel community.

"Because KVM is integrated into the Linux kernel, it takes full advantage of the operating environment," Red Hat explains in a blog entry. "This includes hardware and application support. Hardware and software certified on Red Hat Enterprise Linux 5 should be transparently certified for virtual guests as well. System tools, including management, SELinux security and Red Hat Network all work in both physical, virtual, host and guest deployments."

Red Hat was previously closely aligned with the popular Xen virtualization solution and made Xen a core part of Red Hat Enterprise Linux 5, which was released in 2007. Over the past few years, Red Hat's allegiances have shifted towards KVM for reasons that are likely both technical and political. XenSource, the company behind Xen, was acquired by Citrix in late 2007. The close ties between Citrix and Microsoft could potentially have created some challenges for Red Hat.

The Linux vendor developed an interest in KVM and began contributing to the project. Last year, Red Hat's virtualization strategy got a major boost when the company acquired Qumranet, the company behind KVM. Red Hat started down a path of gradually shifting its enterprise software ecosystem from Xen to KVM. The introduction of KVM in RHEL 5.4, which makes Red Hat's stand-alone KVM virtualization solution a standard part of the enterprise distro, is a noteworthy milestone in that transition.

"Red Hat Enterprise Linux plays a significant role in Red Hat's virtualization strategy," said Red Hat platform business unit vice president Scott Crenshaw in a statement. "The availability of Red Hat Enterprise Linux 5.4 with the same virtualization technology base as Red Hat Enterprise Virtualization today is a significant step in our delivery of virtualization to the market."

Xen will likely be phased out in favor of KVM for RHEL 6. This move won't leave Red Hat's current Xen users out in the cold, however, because the lengthy duration of Red Hat's support cycle will ensure that it continues to be maintained in RHEL5 for years to come. There is also a nifty tool called Xenner that makes it possible to run a Xen kernel and lightweight Xen emulator inside of a KVM guest environment without requiring the Xen hypervisor. Red Hat's virtualization management tools, including oVirt, support both Xen and KVM.