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01 April 2010, 14:18

What's new in Red Hat Enterprise Linux 5.5

Red Hat Logo by Thorsten Leemhuis

Optimised virtualisation, support for recently introduced AMD and Intel processors, new versions of OpenOffice, PostgreSQL and Samba as well as numerous fresh drivers are all among the major advancements of RHEL 5.5.

After releasing a beta version in early February, Red Hat has now released version 5.5 of Red Hat Enterprise Linux (RHEL). As usual at the first stage in the life cycle of this Linux distribution for corporate customers, the new version not only offers new drivers and various corrections, but also numerous new features.

Fine tuning

The developers have added many improvements to the virtualisation functions – especially to the KVM (Kernel-based Virtual Machine) hypervisor. Seven months ago, Red Hat integrated KVM as a second, parallel option to Xen, with the release of version 5.4. Series 6 of RHEL, which is currently in development, will probably use exclusively KVM and SUSE Linux Enterprise (SLES) 11 also plans to officially support KVM in future.

Variants and versions

Customers with support contracts can immediately download the new RHEL via the Red Hat Network; those who already have RHEL5 installed can simply update their version to RHEL 5.5 via Yum or the Red Hat Network.

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

Various vendors and projects offer RHEL clones; probably the most popular among them is the free CentOS, which promises full compatibility with the original. Unlike distributions such as Scientific Linux, CentOS tends to avoid adding functions that are not included in the original RHEL. About six weeks to three months usually pass between the release of a new RHEL version and that of the respective CentOS clones; CentOS 5.4, for instance, became available seven weeks after RHEL 5.4.

Managing KVM guests via the Cluster Suite is now fully supported. Libvirt is now better at handling more than 256 guest systems and automatically tries to use huge pages; this is designed to reduce the memory management overhead and significantly increase performance, especially with modern processors.

Many improvements affect the pass through of either whole PCI/PCIe devices or at least some of their functions, to guest systems; this allows PCI/PCIe components to be withdrawn from one guest system and allocated to another at run time. Red Hat has also integrated drivers for various 10-GB network chips with SR-IOV support into the kernel. These and various further optimisations will also benefit version 2.2 of Red Hat Enterprise Virtualization, which was recently released as a beta and will use the RHEL 5.5 kernel.

Good timing

The kernel and various other components have been extended to support Intel's Boxboro-EX and Boxboro-MC platforms as well as AMD's Magny-Cours 6000 and IBM's Power7 platforms. This means that the Linux distribution is well equipped not only for AMD's 12-core Opteron processors, which were introduced last Monday, but also for the eight-core processors in Intel's Xeon 6500 and 7500 (Nehalem-EX) series introduced a day later.

As usual, the Red Hat developers have added many new and improved drivers to their rather dusted-down Linux 2.6.18-based kernel – by updating the ALSA drivers, for instance, they hope to significantly improve the support of HD-Audio (HDA). Many drivers for Wi-Fi chips were also added or updated; for instance, RHEL now supports Intel's series iwl1000 and iwl6000 Wi-Fi hardware and offers the ath9k driver for recent Atheros chips. Red Hat also updated various storage drivers.


A major version jump upgraded OpenOffice from version 2.3.0 to 3.1.1; the new office suite is said to improve the data exchange with Microsoft Office 2007 in particular. Samba 3.3 should provide Improved cooperation with Windows 7. Samba 3.3 can be found in the "samba3x" packages; the previously used Samba 3.0 is also included to give system admins a choice between the two versions.

PostgreSQL 8.4 is contained in the packages which start with "postgresql84". Originally, the new PostgreSQL was supposed to replace PostgreSQL 8.1, which came with earlier versions of RHEL5 – however, due to minor incompatibilities between the two Red Hat decided to abandon this plan. Administrators can now also choose between the series 1 and series 2 versions of FreeRADIUS.

A new addition in this context is the gPXE network boot loader; other changes include improved kick-start mechanisms for fully or partially automated installation routines as well as the GDB, Valgrind and SystemTap debugging technologies. Details of these and many other advancements of RHEL 5.5 can be found in the release notes (HTML, HTML single page, PDFPDF). Those who want to find out which exact new features are contained in which individual packages can consult the technical notes (HTML, HTML single page, PDFPDF).

Meanwhile, Red Hat's Bugzilla, the Fedora mailing lists and services such as Twitter offer more and more evidence that Red Hat is busily working on Red Hat Enterprise Linux 6; several of the presentations at the next Red Hat Summit to be held in Boston in June will discuss the next major version series of RHEL. If Red Hat continue with their usual development routine, at least one, or possibly even two public betas of RHEL6 should become available in the next few months. However, the vendor has not so far specified a release date for RHEL6 – although a lot currently points towards the second half of 2010. (thl)

Version scheme

Red Hat Enterprise Linux 5.5 offers numerous bug fixes and new drivers for RHEL5. At first glance, this makes "minor releases" such as this fifth edition of RHEL5 appear similar to a Windows Service Pack. However, RHEL5 is still in the first, "Production 1", phase of the "Red Hat Enterprise Linux Life Cycle". In this phase, new versions (such as RHEL 5.5) of a major release (such as RHEL 5) are also given many new features – far more than are usually included in a Service Pack for Windows.

On the other hand in terms of the distribution's basic software – such as the Linux kernel or the glibc – Red Hat tends to avoid major jumps to new versions. The RHEL 5.5 kernel, like that of RHEL 5.0, is therefore based on the rather dusted-down kernel version 2.6.18. However, the Red Hat kernel does differ in many ways from the Linux kernel 2.6.18 available at, because the Red Hat developers have already integrated a vast number of advancements from current versions of the Linux kernel. This includes many drivers for recent hardware, as the drivers included in Linux 2.6.18 are unsuitable or insufficient for many modern systems. Red Hat is not as strict with desktop software such as Evolution, Firefox, OpenOffice or Thunderbird, occasionally updating programs to their current versions as part of a new release.

Systems with a series 5 version of RHEL will be offered the updated RHEL 5.5 software packages as regular updates when the new version is released. If all the updates offered are installed, the system will automatically switch to the latest version of RHEL; however, those who only install the security updates will only receive parts of RHEL 5.5 over time.

Some corporate customers try to avoid this: They fear that, in a new version, new bugs might have been introduced together with the improvements. For some releases, Red Hat therefore offers a separate update channel on the Red Hat network, where security updates and bug fixes for the now obsolete version (currently RHEL 5.3) are available at a charge for several months; Red Hat calls this version series the Z-stream.

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