Revisiting RHEL Clones

Shortly after Red Hat split the freely available Red Hat Linux into a community-like Fedora Project and a high-end Red Hat Enterprise Linux (RHEL), a new breed of Linux distributions emerged - the clones of RHEL. With source packages for RHEL freely available on Red Hat's download servers, several user communities and small businesses started building what is essentially a re-packaged Red Hat Enterprise Linux - complete with security updates, but without the expensive support contract that comes with the real thing. We looked at the early attempts of some of these projects about a year ago. With the release of RHEL 4 earlier this year, this might be a good time to check how far they have progressed and what they are offering today.

If traffic on the CentOS mailing lists is anything to go by, then clearly, there is much demand for these distributions. The number of mailing list posts increased dramatically after the release of CentOS 4.0 and is now reaching the levels normally found only on those of major distributions; in contrast, Red Hat's own mailing lists see hardly any traffic. As one satisfied CentOS user put it, it is not just the cost factor that had attracted him to CentOS, but also the level of free community support available on the lists. Another reason why some users might prefer a RHEL clone over, say, Fedora is that Fedora is sometimes perceived as just a beta release of RHEL; in fact the developers of Lineox Enterprise Linux have noted that 87% of packages in Fedora Core 3 final were passed on to RHEL 4 Beta 2 without any modifications.

The above-mentioned CentOS distribution has now become a de facto standard among the RHEL clones. Although donations are encouraged, this is a pure community projects with no strings attached, and excellent infrastructure in terms of community support and download mirrors. More importantly, CentOS is building a complete set of releases for all architectures supported by RHEL (at the time of writing, i386, ia64 and x86_64 builds are completed, while ppc, s390 and s390x are expected to follow). CentOS is also the purest rebuild where the only modifications done to the original source packages were those that required the removal of Red Hat logos and trademarks. Security updates are handled by up2date and CentOS Networks. These tend to be released fairly promptly; checking the difference between the time a security update was announced by Red Hat and the time the said update was released by CentOS, we found that this process normally takes between 1 and 7 days.

Lineox Enterprise Linux is another popular RHEL clone. Built by a Finland-based company of the same name, Lineox is a commercial product which provides free CD/DVD ISO images for download, but charges a modest fee for security updates (€5 - 15 per system per year, depending on the number of systems). This seems to be a successful business model that might appeal to users willing to pay a small price in order to provide an incentive for the company to continue the update service. Lineox is extremely fast in building security updates - these are normally available within 24 hours after they are released upstream by Red Hat. The distribution has replaced the up2date infrastructure with apt and yum (with Synaptic and Yumex as their respective graphical front-ends) with apt being the preferred update method. Yum is only provided in the x86_64 edition - this is because apt does not work well with systems that contain a mix of 32-bit and 64-bit applications and libraries.

Scientific Linux is a relatively new entry among the RHEL clones. Developed by a collaborative effort at several universities in the United States, Switzerland and other countries, Scientific Linux is a free community project that not only rebuilds the source packages for RHEL, it also adds a handful of enhancements. Browsing through its download directory we spotted a few packages that are missing from RHEL, including the Pine mail client, XMMS with MP3 support, and OpenAFS - a distributed file system product which IBM has handed over to the open source community for development and maintenance. Security updates in Scientific Linux are provided reasonably fast, usually within a week of upstream updates. Scientific Linux 4.0 is currently in development - the i386 edition has reached a release candidate stage, while the x86_64 edition is in early alpha.

Tao Linux is another community project attempting to compile the RHEL source RPMs into installable CD and DVD images. Although not nearly as popular as CentOS, its mailing lists are reasonably busy and, like CentOS, it provides builds for all architectures supported by Red Hat. Security updates, handled via yum, are released extremely fast - often faster than those by CentOS. The i386 edition of Tao Linux 4 has been in beta testing for a couple of weeks, so it shouldn't be long before we see a final release. It is not clear whether the developers plan to provide version 4 for non-i386 architectures.

Pie Box Enterprise Linux is yet another RHEL clone. This is a commercial product by the UK-based PixExcel and not available for free download. Updates, charged at £15 per system per year, are provided via a custom edition of yum, which has to be downloaded separately. This product is similar to CentOS in that there are no modifications made to the original sources other than the removal of Red Hat logos and trademarks. At this time, only a i386 edition of Pie Box Enterprise Linux is available.

Other distributions that set out on the same path as the above five have yet to produce a new release based on RHEL 4. The best-known among them is White Box Enterprise Linux, the developers of which are reportedly working on version 4. The project's reputation has been somewhat tarnished by falling behind on providing security updates, although lately they seem to have improved in this department. There are several other projects that have released distributions based on RHEL 3, but no yet given an indication about their future plans. Nevertheless, both X/OS Linux and Fermi Linux continue to provide timely security updates for their existing products. In contrast, Eadem Enterprise Linux has fallen behind in recent months, while StartCom Enterprise Linux has not published any security updates since September last year.

Conclusion? If you are in this market, your best bet is probably CentOS or Scientific Linux, both of which are excellent, free community projects that are likely to be around for some time. Lineox and Tao Linux are very fast in terms of providing security updates, and could also be considered, but bear in mind that both are essentially "one-man" projects, which is not very reassuring when you have to rely on a single person to provide security updates for the next 5 years. Also, if Red Hat releases a new RHEL version every 18 months, with each of them having a life span of 5 years, it can be tedious for a single person to support so many different releases for several architectures. As for Pie Box, it is comparatively expensive since both the installation media and security updates require cash outlay. The remainder of the distributions listed above have not yet produced a new release based on RHEL 4, but both X/OS Linux and Fermi Linux continue supporting their older releases.

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GuestArticles	Bodnar, Ladislav

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