2009-11-25 12:39:26 
阿炯
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.
Red Hat把免费的Red Hat Linux产品分割成一个类社区的Fedora项目和高端Red Hat Enterprise Linux(RHEL)，故而派生出新一代的Linux发行版——RHEL的克隆。RHEL免费包来源在Red Hat的下载服务器，多个用户社区和小型企业开始构建一个本质上是重新包装RHEL，配有安全更新，但是没有带来的昂贵的支持合同。随着RHEL 4发布的今年早些时候，我们来看一下它们提供的产品进展如何。
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.
CentOS Linux 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.
Oracle Linux，正式名称为甲骨文企业Linux(Oracle Enterprise Linux)，为甲骨文公司(Oracle)所发布的企业级Linux，其建基于Red Hat Enterprise Linux。首次发布于2006年10月25日。其免费供应于大众下载、使用与发布，并为Red Hat版Linux用户提供有偿支持。Oracle Linux有两种内核：兼容Red Hat Enterprise Linux的内核(使用RHEL源代码编译)和Oracle自己的Unbreakable Enterprise内核。Oracle声明Unbreakable Enterprise内核兼容RHEL，Oracle中间件和经过RHEL认证的第三方应用程序可以不经过修改的在Unbreakable Enterprise内核上运行。软件包管理系统：RPM Package Manager 或 YUM方式。
Fedora Linux，在第七版以前为Fedora Core，是较具知名度的Linux发行包之一，由Fedora项目社区开发、红帽公司赞助，目标是创建一套新颖、多功能并且自由(开放源代码)的操作系统。Fedora是商业化的Red Hat Enterprise Linux发行版的上游源码。对于一般用户而言，是一套功能完备、更新快速的免费操作系统；而对赞助者Red Hat公司而言，它是许多新技术的测试平台，被认为可用的技术最终会加入到Red Hat Enterprise Linux中。Fedora大约每六个月发布新版本，而每个版本目前提供约13个月的更新维护，使用已停止支持版本的用户必须升级至新版本才能获得更新。
Enterprise Linux额外软件包(Extra Packages for Enterprise Linux，EPEL)是由来自Fedora Project的志愿者发起的社区力量，为了创建由高质量的附加软件组成的、用于补足RHEL和其他兼容版本的软件仓库。软件包管理主要由yum实用程序提供，在22版后则由dnf取代。Fedora同样提供图形界面(例如pirut，pup和puplet)，用于在更新可用时提供视觉通知。apt-rpm是yum的替代品，对于Debian类发行版的用户来说可能更熟悉。APT被用于管理软件包，额外的软件仓库可以被添加到Fedora，以便安装Fedora软件仓库未提供的软件包。
在Fedora 7之前，有Core和Extras两个主要的仓库。Fedora Core仓库包含所有操作系统必需的基本软件包，以及其他随安装CD/DVD发行的、由Red Hat开发者维护的软件包。Fedora Extras仓库自Fedora Core 3开始加入，包含社区维护的、没有随安装CD/DVD发布的软件包。自Fedora 7开始，Core和Extras软件仓库被合并，因此该版本在其名称中去掉了Core。该软件仓库同样允许社区成员维护的软件包，这在以前是Red Hat开发者才可进行的。在Fedora 7发布之前，有一个叫做Fedora Legacy的第三方软件仓库。该软件仓库主要包含社区维护的、针对较老的Fedora和选中的Red Hat发行版，用于延长这些版本的生命周期。Fedora Legacy于2006年12月关闭。
安全是Fedora中最重要的功能。其中一项是SELinux——基于内核中的Linux Security Modules(LSM)的、补充了各种安全策略的Linux功能，包括访问控制等。Fedora是引领SELinux的发行版之一，SELinux包含于Fedora Core 2和以后的发行版。默认情况下，该功能强制修改系统的运作方式，因此处于关闭状态，但在SPARC上启用。
Fedora 33 于2020年10月27日正式发布，用户将可获得开源社区提供的多个 Fedora 版本的最新版，总体改进包括：
其中更新了关键的编程语言和系统库软件包，包括 Python 3.9，Ruby on Rails 6.0 和 Perl 5.32。
在 Fedora KDE 中跟踪 Fedora 32 Workstation 中的工作，并默认启用了 EarlyOOM 服务，以改善低内存情况下的用户体验。
将 nano 设置为默认编辑器，工作站版本(Workstation)使用 BTRFS 为默认文件系统。
针对不同版本的介绍及更新：
Fedora Editions 针对台式机、服务器和云环境中的特定“showcase”功能，现在也适用于物联网。
Fedora Workstation 专注于台式机，此发行版具有 GNOME 3.38 的功能。视觉方面，Fedora 33 Workstation 现在默认提供动画背景。
Fedora CoreOS 是一个新兴的 Fedora 版本，它提供了几个更新流，可以跟踪大约每两周发生一次的自动更新，下一个流基于 Fedora 33 ，接下来是测试和稳定流。
Fedora IoT，最新提升为 Edition 级别，适用 IoT 生态系统和边缘计算。Fedora 33 IoT 引入了“Platform AbstRaction for SECurity(PARSEC)”，这是一项开源计划，旨在以与平台无关的方式为硬件安全和加密服务提供通用 API。
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.
总结(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.