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 support x86 with Physical Address Extension (PAE), with additional architectures supported in CentOS versions older than 4.7; a beta release is expected to be available for the ARM architecture.
Before it adopted the “CentOS” name, CentOS Linux originated as a build artifact of cAos Linux. Several of the cAos contributors at the time[when?] 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.
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
Before version 7.0, CentOS version numbers have two parts, a major version and a minor version, which correspond to the major version and update set of Red Hat Enterprise Linux that was used to build that version of CentOS. 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 the third part that indicates 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[update]) 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).