Red Hat Enterprise Linux (often incorrectly abbreviated to RHEL) is a Linux distribution produced by Red Hat and targeted toward the commercial market, including mainframes. Red Hat commits to supporting each version of RHEL for 7 years after its release. All of Red Hat's official support, all of Red Hat's training and the Red Hat Certification Program center on the Red Hat Enterprise Linux platform.

New versions of RHEL are released every 18 to 24 months. When Red Hat releases a new version of RHEL, customers may upgrade to the new version at no extra charge as long as they are in possession of a current subscription (i.e. the subscription term has not yet lapsed).

Red Hat's first Enterprise offering (Red Hat Linux 6.2E) essentially consisted of a version of Red Hat Linux 6.2 with different support levels, and without separate engineering.

The first version of RHEL to resemble the name originally came onto the market as "Red Hat Linux Advanced Server". In 2003 Red Hat rebranded Red Hat Linux Advanced Server to "Red Hat Enterprise Linux" (RHEL) AS, and added two more variants, RHEL ES and RHEL WS.

Verbatim copying and redistribution of the entire RHEL distribution is not permitted due to trademark restrictions. However, there are several redistributions of RHEL minus trademarked features (such as logos and the name).

Variants

As of 2005 Red Hat distributed four variants of RHEL (AS/ES/WS expansions are unofficial):

RHEL AS (“Advanced Server”) – for mission-critical/enterprise computer systems.

RHEL ES (“Edge Server”, “Economy Server”, or “Entry-level Server”) – for supported network servers

RHEL WS (“Workstation”) – for technical power-user desktops or high-performance computing

Red Hat Desktop – for multiple deployments of single-user desktops

There are also "Academic" editions of the Desktop and Server variants. They are offered to schools and students, are less expensive, and are provided with Red Hat technical support as an optional extra. Web support based on number of customer contacts can be purchased separately.

People sometimes mistakenly refer to ES as "Enterprise Server", in contrast to AS (Advanced Server). This may be because Novell has a server distribution called SUSE Linux Enterprise Server (SLES). However, nowhere on its site or in its literature does Red Hat say what AS, ES and WS stand for.

In RHEL 5 there are new editions that substitute former RHEL AS/ES/WS/Desktop:

RHEL Advanced Platform (former AS)

RHEL (former ES)

RHEL Desktop with Workstation and Multi-OS option

RHEL Desktop with Workstation option (former WS)

RHEL Desktop with Multi-OS option

RHEL Desktop (former Desktop)

Red Hat also announced its Red Hat Global Desktop Linux edition "for emerging markets"

Relationship to free or community distributions

Originally, Red Hat based RHEL on Red Hat Linux, but using a much more conservative release cycle. Later versions leveraged technologies from Fedora which is a community distribution and project that Red Hat sponsors. Roughly every third version of Red Hat Linux (RHL) or Fedora forms the basis for a version of RHEL, thus:

RHL 6.2 → RHL 6.2E

RHL 7.2 → RHEL 2.1

RHL 9 → RHEL 3

FC 3 → RHEL 4

FC 6 → RHEL 5

Fedora 9 → RHEL 6 (projected)

Rebuilds

Main article: Red Hat Enterprise Linux clones

Originally, Red Hat's enterprise product, then known as Red Hat Linux, was made freely available to anybody who wished to download it, while Red Hat made money from support. Red Hat then moved towards splitting its product line into Red Hat Enterprise Linux which was designed to be stable and with long-term support for enterprise users and 'Fedora' as the community distribution and project sponsored by Red Hat. They use trademarks to prevent verbatim copying of Red Hat Enterprise Linux. However, some people[attribution found the new products lacking: those who could not afford or did not wish to pay for enterprise-level support but valued the stability and long-term update cycle of the enterprise product.

Since Red Hat Enterprise Linux is based completely on free and open source software, Red Hat makes available the complete source code to its enterprise distribution through its FTP site to anybody who wants it. Accordingly, several groups have taken this source code and compiled their own versions of Red Hat Enterprise Linux, typically with the only changes being the removal of any references to Red Hat's trademarks and pointing the update systems to non-Red Hat servers. Groups which have undertaken this effort include CentOS (the most popular as of June 2007), StartCom Enterprise Linux, Pie Box Enterprise Linux, Scientific Linux, White Box Enterprise Linux and Lineox. Oracle Corporation has also recently come out with its own repackaging of Red Hat Enterprise Linux called Oracle Enterprise Linux as part of its Unbreakable Linux program but does not provide a free mechanism for applying updates without paying a service fee as with Red Hat.

Rebuilds of RHEL are free but do not get any commercial support or consultancy services from Red Hat and lack any software, hardware or security certifications. Also, the rebuilds do not get access to Red Hat services like Red Hat Network .

Commercial products based on Red Hat Enterprise Linux

Main article: Commercial products based on Red Hat Enterprise Linux

A number of commercial vendors use Red Hat Enterprise Linux as a base for the operating system in their products. The most well-known is the Console Operating System in VMware ESX Server.

Version history

RHL 6.2E (Zoot), 27 March 2000

RHEL 2.1 AS (Pensacola), 26 March 2002

RHEL 2.1 ES (Panama), May 2003

RHEL 3 (Taroon), 22 October 2003

Update 1, 16 January 2004

Update 2, 18 May 2004

Update 3, 3 September 2004

Update 4, 21 December 2004

Update 5, 20 May 2005

Update 6, 28 September 2005

Update 7, 15 March 2006

Update 8, 20 July 2006

Update 9, 15 June 2007

RHEL 4 (Nahant), 15 February 2005

Update 1, 9 June 2005

Update 2, 5 October 2005

Update 3, 7 March 2006

4.4 (also known as Update 4), 11 August 2006

4.5 (also known as Update 5), 1 May 2007

4.6 (also known as Update 6), 15 November 2007

RHEL 5 (Tikanga), 14 March 2007

5.1 (also known as Update 1), 7 November 2007

Software included in RHEL 5

Linux 2.6.18

Apache 2.2.3

MySQL 5.0.22

PHP 5.1.6

PostgreSQL 8.1.4

GNOME 2.16

KDE 3.5.4