about CentOS

CentOS (abbreviated from Community Enterprise Operating System) is a Linux distribution that attempts to provide a free,enterprise-class,

community-supported computing platform which aims to be functionally compatible with its upstream source,Red Hat Enterprise Linux (RHEL). In January 2014, CentOS announced the official joining with Red Hat while staying independent from RHEL, under a new CentOS governing board.

The first CentOS release in May 2004, numbered as CentOS version 2, was forked from RHEL version 2.1AS. Since the release of version 7.0, CentOS officially supports only the x86-64 architecture, while versions older than 7.0-1406 also supportIA-32 with Physical Address Extension (PAE), with additional architectures supported in CentOS versions older than 4.7. As of June 2015, beta releases of CentOS 7 are available for the IA-32 architecture and for the AArch64 variant of the ARM architecture.

History

Prior to becoming known under its current name, CentOS originated as a build artifact of cAos Linux. At the time,some of the cAos contributors were merely interested in this build artifact for their own use, citing difficulties in collaborating with other noteworthy Red Hat Enterprise Linux (RHEL) clones of the time.

In June 2006, David Parsley, the primary developer of Tao Linux (another RHEL clone), announced the retirement of Tao Linux and its rolling into CentOS development. Tao's users migrated to the CentOS release via yum update.

In July 2009, it was reported in an open letter on the CentOS project web site that CentOS's founder, Lance Davis, had disappeared in 2008. Davis had ceased contribution to the project, but continued to hold the registration for the CentOS domain and PayPal account. In August 2009, the CentOS team reportedly made contact with Davis and obtained the centos.info and centos.org domains.

In July 2010, CentOS overtook Debian to become the most popular Linux distribution for web servers, with almost 30% of all Linux web servers using it. (Debian retook the lead in January 2012.)

In January 2014, Red Hat announced that it would sponsor the CentOS project, "helping to establish a platform well-suited to the needs of open source developers that integrate technologies in and around the operating system". As the result of these changes, ownership of CentOS trademarks was transferred to Red Hat, which now employs most of the CentOS head developers; however, they work as part of the Red Hat's Open Source and Standards team, which operates separately from the Red Hat Enterprise Linux team. A new CentOS governing board was also established.

Design

RHEL is available only through a paid subscription service that provides access to software updates and varying levels of technical support. The product is largely composed of software packages distributed under free software licenses and the source code for these packages is made public by Red Hat.

CentOS developers use Red Hat's source code to create a final product very similar to RHEL. Red Hat's branding and logos are changed because Red Hat does not allow them to be redistributed. CentOS is available free of charge. Technical support is primarily provided by the community via official mailing lists, web forums, and chat rooms.

The project is affiliated with Red Hat but aspires to be more public, open, and inclusive. While Red Hat employs most of the CentOS head developers, the CentOS project itself relies on donations from users and organizational sponsors.

Versioning and releases

CentOS releases

CentOS version numbers for releases older than 7.0 have two parts, a major version and a minor version, which correspond to the major version and update set of Red Hat Enterprise Linux (RHEL) used to build a particular CentOS release. For example, CentOS 6.5 is built from the source packages of RHEL 6 update 5 (also known as RHEL version 6.5), which is a so-called "point release" of RHEL 6.

Starting with version 7.0, CentOS version numbers also include a third part that indicates the monthstamp of the source code the release is based on. For example, version number 7.0-1406 still maps this CentOS release to the zeroth update set of RHEL 7, while "1406" indicates that the source code this release is based on dates from June 2014. Using the monthstamp allows installation images to be reissued for (as of July 2014) oncoming container and cloud releases, while maintaining a connection to the related base release version.

Since mid-2006 and starting with RHEL version 4.4, which is formally known as Red Hat Enterprise Linux 4.0 update 4, Red Hat has adopted a version-naming convention identical to that used by CentOS (for example, RHEL 4.5 or RHEL 6.5).

Add-ons releases

Software Collections (SCL) is a CentOS repository that provides a set of dynamic programming languages, database servers, and various related packages. Provided software versions are either more recent than their equivalent versions included in the base CentOS distribution, or are made available as official CentOS packages for the first time.(See also the list of CentOS repositories below.)

Packages available from the SCL do not replace the default system tools provided with CentOS. Instead, a parallel set of tools is installed in the /opt directory, and can be optionally enabled per application by using supplied scl utility. For example, the default versions of Perl or MySQL remain those provided by the base CentOS installation.

End-of-support schedule

In accordance with the Red Hat Enterprise Linux life cycle, CentOS 5, 6 and 7 will also be supported for ten years. Previously, CentOS 4 had been supported for seven years.

CentOS version	Release date	Full updates	Maintenance updates
3	19 March 2004	20 July 2006	31 October 2010
4	9 March 2005	31 March 2009	29 February 2012
5	12 April 2007	Q1 2014	31 March 2017
6	10 July 2011	Q2 2017	30 November 2020
7	7 July 2014	Q4 2020	30 June 2024
Old version Older version, still supported Latest version

Releases without upstream equivalents

Some of the ISO images released by the CentOS project have no direct upstream equivalents. They are created for specific purposes, such as for providing a live bootable image, or for providing a reduced-size installation media.

LiveCD and LiveDVD images contain a bootable compressed file system, created by a set of custom scripts using a kickstart configuration file. These live images can be also installed to hard disk, thus obtaining a fully functional CentOS installation. The set of packages installed that way on a hard disk can not be adjusted during the installation, as that is a simple transfer of the image existing on CD/DVD, to a hard disk. After booting from hard disk, yum can be used for adding or removing packages.

MinimalCD images contain a minimum of packages required for a functional installation, with no compromises in security or network usability. These minimal images use the standard CentOS installer with all of its regular features minus the selection of packages. Yum can be used after the installation is completed to add or remove packages.

Special interest groups

Special interest groups (SIGs) are organized portions of the CentOS community that open paths for building specialized variants of CentOS, which fulfill specific sets of requirements. SIGs have the freedom to modify and enhance CentOS in various ways, including adding more cutting-edge software, rebuilding existing packages depending on the requirements, providing alternative desktop environments, or making CentOS available on otherwise unsupported architectures. This provides an opportunity for the community to get the best of both worlds – the overall stability of CentOS and newer technology from various open-source projects.

Architectures

As of version 7, CentOS fully supports only the x86-64 architecture, while the following architectures are not supported:

• IA-32 in all variants, not supported since CentOS 7
• IA-32 without Physical Address Extension (PAE), not supported since CentOS 6
• IA-64 (Intel Itanium architecture), supported in CentOS 3 and 4
• PowerPC/32 (Apple Macintosh and PowerMac running the G3 or G4 PowerPC processor), beta support available in CentOS 4
• IBM Mainframe (eServer zSeries and S/390), not supported since CentOS 5
• Alpha, support available in CentOS 4
• SPARC, beta support available in CentOS 4

Since May 2015, a beta release of CentOS 7 is available for the AArch64 architecture, and plans exist for supporting other variants of the ARM architecture. ARM support is a community effort coordinated through the AltArch SIG. Since June 2015, a beta release of CentOS 7 is also available for the IA-32 architecture.

A Live CD version of CentOS is available at mirror.centos.org. A Live USB of CentOS can be created manually or with UNetbootin.

CentOS images are also available on Amazon's EC2 cloud, in form of prebuilt and already published Amazon Machine Images (AMIs).

Repositories

There are three primary CentOS repositories (also known as channels), containing software packages that make up the main CentOS distribution:

• base – contains packages that form CentOS point releases, and gets updated when the actual point release is formally made available in form of ISO images.
• updates – contains packages that serve as security, bugfix or enhancement updates, issued between the regular update sets for point releases. Bugfix and enhancement updates released this way are only those unsuitable to be released through the CentOS-Fasttrack repository described below.
• addons – provides packages required for building the packages that make up the main CentOS distribution, but are not provided by the upstream.

The CentOS project provides several additional repositories that contain software packages not provided by the default base and updates repositories. Those repositories include the following:

• CentOS Extras – contains packages that provide additional functionality to CentOS without breaking its upstream compatibility or updating the base components.
• CentOSPlus – contains packages that actually upgrade certain base CentOS components, changing CentOS so that it is not exactly like the upstream provider's content.
• CentOS-Testing – serves as a proving ground for packages on their way to CentOSPlus and CentOS Extras. Offered packages may or may not replace core CentOS packages, and are not guaranteed to work properly.
• CentOS-Fasttrack – contains bugfix and enhancement updates issued from time to time, between the regular update sets for point releases. The packages released this way serve as close candidates for the inclusion into the next point release. This repository does not provide security updates, and does not contain packages unsuitable for uncertain inclusion into point releases.
• CR (Continuous Release) – makes generally available packages that will appear in the next point release of CentOS. The packages are made available on a testing and hotfix basis, until the actual point release is formally released in form of ISO images.
• debuginfo – contains packages with debugging symbols generated when the primary packages were built
• contrib – contains packages contributed by CentOS users that do not overlap with any of the core distribution packages
• Software Collections – provides versions of software newer than those provided by the base distribution, see above for more details