CentOS

CentOS is a freely-available Linux distribution that is based on Red Hat's commercial product: Red Hat Enterprise Linux (RHEL). This rebuild project strives to be 100% binary compatible with the upstream product and, within its mainline and updates, not to vary from that goal. Additional software archives hold later versions of such packages, along with other Free and Open Source Software RPM-based packages. 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 paying 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 that 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 that 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 CentOS Mirror Network.

CentOS can be used as an X Window System-based desktop but, like RHEL, is targeted primarily at the server market. Some hosting companies rely on CentOS working together with the cPanel Control Panel.

Versioning scheme
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-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. CentOS refers to the source as "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 project members regarding possible trademark issues.
-Since mid-2006, starting with RHEL 4.4 (formerly known as RHEL 4.0 update 4), Red Hat have adopted a versioning convention identical to that of CentOS, e.g., RHEL 4.5 or RHEL 3.9. See this Red Hat Knowledge Base article for more information.

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