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CentOS is a freely available Linux distribution which is based on Red Hat's commercial Red Hat Enterprise Linux (RHEL) product. This rebuild project strives to be 100% binary compatible with the upstream product, and within its mainline and updates, to not vary from that goal. Additional software archives hold later versions of such packages, along with other Free and Open Source Software RPM based packagings. CentOS stands for Community ENTerprise Operating System.
RHEL is largely composed of free and open source software, but is made available in a usable, binary form (such as on CD-ROM or DVD-ROM) only to paid subscribers. As required, Red Hat releases all source code for the product publicly under the terms of the GNU General Public License and other licenses. CentOS developers use that source code to create a final product which is very similar to RHEL and freely available for download and use by the public, but not maintained or supported by Red Hat. There are other distributions derived from RHEL's source as well, but they have not attained the surrounding community which CentOS has built; CentOS is generally the one most current with Red Hat's changes.
CentOS preferred software updating tool is based on yum, although support for use of an up2date variant exists. Each may be used to download and install both additional packages and their dependencies, and also to obtain and apply periodic and special (security) updates from repositories on the [http://www.centos.org/modules/tinycontent/index.php?id=13 CentOS Mirror Network].
CentOS can be used for a X Window based desktop, but is targeted primarily as the server market, like RHEL. Many big name hosting companies rely on CentOS working together with the cPanel Control Panel.
Versioning scheme
CentOS version numbers have two parts, a major version and a minor version. The major version corresponds to the version of Red Hat Enterprise Linux from which the source packages used to build CentOS are taken. The minor version corresponds to the update set of that Red Hat Enterprise Linux version from which the source packages used to build CentOS are taken. For example, CentOS 4.4 is built from the source packages from Red Hat Enterprise Linux 4 update 4.
Release history
The first version of CentOS, CentOS 3 build4-rc0, was released in the end of 2003. CentOS 3.1 (version 3, quarterly update 1) was released on March 19, 2004 [http://lists.centos.org/pipermail/centos/2004-March/000015.html]. CentOS 2, based on version 2.1 of Red Hat Enterprise Linux, was released on May 14, 2004 [http://lists.centos.org/pipermail/centos/2004-May/000153.html]. CentOS 4.0, based on Red Hat Enterprise Linux version 4, was released for the i386 architecture [http://www.centos.org/modules/news/article.php?storyid=71] and for the ia64 architecture on March 1, 2005.
Architectures
CentOS supports all the same architectures as Red Hat Enterprise Linux, and adds some as well (Alpha, Sparc).
* Intel x86-compatible (32 bit)
* Intel IA-64 (64 bit)
* Advanced Micro Devices AMD64 and Intel EM64T (64 bit)
* PowerPC/32 (Apple Macintosh PowerMac running the G3 or G4 PowerPC processor) ("beta" support)
* IBM Mainframe (eServer zSeries and S/390)
There is also support for 2 architectures not supported upstream at the PNAELV (Prominent North American Enterprise Linux Vendor), which is an acronym referring to Red Hat, coined in response to questions raised by Red Hat's legal counsel in a letter to two project members as to possible Trade Mark (mis-)use issues:
* Alpha
* SPARC ("beta" support)
Distributions based on CentOS
* [http://www.nuonce.net/bq-cd.php NuOnce Networks CentOS / Blue Quartz CD]
* Rocks Cluster Distribution, for computer clusters, is now based on CentOS
* [http://contribs.org/ SME Server]
* [http://www.trixbox.org/ Trixbox], a PBX solution
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