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04 September 2009, 06:53

What's new in Red Hat Enterprise Linux 5.4

by Thorsten Leemhuis

Red Hat logo At the Red Hat Summit 2009 currently held in Chicago, Red Hat has released version 5.4 of Red Hat Enterprise Linux (usually abbreviated to RHEL) – two months after the pre-release beta, just over seven after version 5.3, and about two and a half years after the introduction of RHEL5. As is customary in the first part of the Red Hat Enterprise Linux life cycle, the new version offers numerous new drivers and various non-security fixes as well as a range of improvements and extensions.


The most outstanding new feature of the fourth major RHEL 5 update is the support of KVM (Kernel-based Virtual Machine) virtualisation, which was integrated into the Linux kernel's main development branch quite a while ago. However, the Linux distributor explicitly points out that the current and any future releases of RHEL5 will continue to support Xen virtualisation. In view of the take-over of KVM developers Qumranet in September last year, the earlier removal of the Xen-Dom0 kernels from Fedora, and the Xen developers' constant struggle to get their technology integrated into the main development branch, however, it looks like Red Hat intends to go for KVM in the long run.

Variants and versions

Customers with support contracts can download the new version via the Red Hat Network as of now. RHEL 5 systems will be offered the new software as a regular update that can, for example, be installed via the "yum update" command.

Red Hat Enterprise Linux  5 is available in three variants: The RHEL 5 Advanced Platform is available for x86-32, x86-64, Itanium, System p (Power) and System z. It allows an unlimited number of virtual guests, supports cluster operation and runs on computers with any number of CPUs. RHEL 5 Server, which is also available for all the platforms mentioned above, is limited to four guest systems and two processor sockets, and comes without the cluster package. RHEL 5 Desktop is available for x86-32 and x86-64 systems in various different configurations: with or without virtualisation, with or without server and development tools, and with various different hardware limits.

In a tweet and in mail, the developers of the probably most popular and, unlike RHEL, free CentOS RHEL clone have already indicated that they will soon start their work on CentOS 5.4. It remains to be seen how long it will take them to catch up this time – after the release of RHEL 4.8, they needed quite a long time to release CentOS 4.8, which was in part caused by internal difficulties which have now largely been resolved.

Red Hat's list of supported KVM guest systems includes all the currently maintained RHEL versions as well as Microsoft Windows XP, Windows Server 2003 and Windows Server 2008. Paravirtualised drivers which considerably improve the I/O performance of guest systems compared to those with full emulation have recently become available for the latter. However, KVM does require processors with virtualisation functionality, although this is available in most of the current AMD and Intel models. Unlike Xen, it does not offer a complete paravirtualisation solution for modified guest systems.

KVM guest systems can be added and managed with the virt-manager – since RHEL5 uses the same tool for Xen, not much has changed for administrators in this respect. Migration tools are being developed to help customers switch from Xen to KVM.

In addition to the KVM hypervisor, the new version also contains the server, the client and the browser plug-in for qspice, a remote rendering technology Qumranet originally intended to market commercially. Also new are the support of Intel's VT-d (Virtualisation Technology for Directed I/O) as well as SRIOV (Single Root I/O for Virtualisation) in KVM and Xen.

New additions

The developers have integrated FUSE (File System in Userspace) support. The SystemTrap tracing and debugging solution was updated and is now "fully supported"; improved analysis is to be available via several static tracepoints located in a number of important RHEL kernel areas. Red Hat reportedly also improved the support of the series 5500 Xeon CPUs and of AMD's Istanbul processor.

The new version offers drivers and tools for Fibre Channel over Ethernet (FCoE) and Clustered Samba as technical previews without official support. Introduced with RHEL 5.3, the support for the Ext4 file system has been updated but it maintains its technical preview status. The same status applies to the GCC 4.4 and the new XFS file system support.


Red Hat have now integrated the Generic Receive Offload (GRO) Infrastructure integrated into the kernel with Linux 2.6.29, as well as several 10-Gigabit network hardware drivers based on it. Further additions are the bnx2i driver and the cnic driver recently merged with Linux 2.6.31 – both drivers address chips by Broadcom. Among the drivers updated by the developers are the bnx2, e1000e, forcedeth, igb, sky2 and tg3 network drivers, which improve the support of recent Broadcom, Intel, Marvell and NVIDIA chips.

Dozens of updates to support new hardware were also made, particularly in the storage driver area. This is only the tip of the iceberg, however, as in their usual fashion, the developers also integrated or updated numerous further drivers in the Linux 2.6.18-based kernel.

In Detail

This article at The H Open only summarises the most important changes of RHEL 5.4. Many further details can be found in the release email, the RHEL 5.4 Technical OverviewPDF, the release notes (HTML/HTML single page, PDFPDF) and the very comprehensive technical notes (HTML/HTML single page, PDFPDF).

In his blog, Red Hat developer Mark Cox has released the Enterprise Linux 5.3 to 5.4 risk report, which provides an overview of the vulnerabilities and security updates made since RHEL 5.3.


Version overview

Like its three immediate predecessors in the RHEL5 series, Red Hat Enterprise Linux 5.4 offers a large number of bug fixes and new drivers. This makes new versions appear similar to a Windows service pack. However, RHEL5 is currently still in the "Production 1" phase of the "Red Hat Enterprise Linux Life Cycle". Updates like RHEL 5.4 are given many new features during this phase – considerably more than a Windows service pack would traditionally offer.

However, in terms of the distribution's basic software – for example the Linux kernel or the Glibc –, Red Hat doesn't make any major new version updates. Like the RHEL 5.0 kernel, RHEL 5.4 is based on the slightly outdated kernel version 2.6.18. However, the Red Hat kernel has become quite different from the Linux kernel 2.6.18 available at, as the Red Hat developers have incorporated countless improvements from more recent kernel versions into their kernel. Among them are many recent hardware drivers, because the Linux 2.6.18 drivers are unsuitable or insufficient for many modern systems.

The Linux distributor isn't quite as strict with desktop software like Evolution, Firefox, OpenOffice or Thunderbird, updating these programs to the latest versions with an occasional new y release ("RHEL x.y" where x=5 and y=4) – RHEL 5.2 was a good example.

Systems with RHEL series 5 are usually offered the software packages updated together with RHEL 5.4 as regular updates. This way, if a system accepts and installs all the updates offered, it will automatically switch to the latest 'y' release. At the latest, a system will begin to incorporate parts of RHEL 5.4 with the installation of any current and future security updates in the coming months.

Some corporate customers want to avoid this: They fear that a new 'y' release may both contain improvements and introduce new bugs. For some 'y' releases, Red Hat therefore offers separate update channels in the Red Hat Network which are subject to a fee and provide security updates and bug fixes (z streams) for the now outdated version (currently RHEL 5.3).

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