Red Hat Enterprise Linux is a Linux distribution
developed by Red Hat and targeted toward the
commercial market. Red Hat Enterprise Linux
is released in server versions for x86, x86-64,
Itanium, PowerPC and IBM System z, and desktop
versions for x86 and x86-64. All of Red Hat's
official support and training and the Red
Hat Certification Program centers around the
Red Hat Enterprise Linux platform. Red Hat
Enterprise Linux is often abbreviated to RHEL,
although this is not an official designation.
The first version of Red Hat Enterprise Linux
to bear 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 AS", and
added two more variants, Red Hat Enterprise
Linux ES and Red Hat Enterprise Linux WS.
Red Hat uses strict trademark rules to restrict
free re-distribution of their officially supported
versions of Red Hat Enterprise Linux, but
still freely provides its source code. Third-party
derivatives can be built and redistributed
by stripping away non-free components like
Red Hat's trademarks, including community-supported
distributions like CentOS and Scientific Linux,
and commercial forks like Oracle Linux, which
aim to offer 100% binary compatibility with
Red Hat Enterprise Linux.
Variants
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.
It is often assumed the branding ES, AS, and
WS stand for "Entry-level Server", "Advanced
Server" and "Work Station", respectively.
The reason for this is that the ES product
is indeed the company's base enterprise server
product, while AS is the more advanced product.
However, nowhere on its site or in its literature
does Red Hat say what AS, ES and WS stand
for.
In Red Hat Enterprise Linux 5 there are new
editions that substitute former Red Hat Enterprise
Linux ASWS/Desktop:
Red Hat Enterprise Linux Advanced Platform
Red Hat Enterprise Linux
Red Hat Enterprise Linux Desktop with Workstation
and Multi-OS option
Red Hat Enterprise Linux Desktop with Workstation
option
Red Hat Enterprise Linux Desktop with Multi-OS
option
Red Hat Enterprise Linux Desktop
Red Hat had also announced its Red Hat Global
Desktop Linux edition "for emerging markets".
RHEL 4, 3, and prior releases had four variants:
Red Hat Enterprise Linux AS for mission-critical/enterprise
computer systems.
Red Hat Enterprise Linux ES for supported
network servers
Red Hat Enterprise Linux WS for technical
power user enterprise desktops for high-performance
computing
Red Hat Desktop for multiple deployments of
single-user desktops for enterprises.
Relationships
Originally, Red Hat sold support for versions
of Red Hat Linux Starting with RHEL 2.1 AS
in 2002, Red Hat sold their first version
of RHEL. It was based on Red Hat Linux, but
used a much more conservative release cycle.
Later versions included technologies from
the Red Hat–sponsored Fedora community distribution
project. Red Hat Enterprise Linux release
schedules do not follow that of Fedora but
are more conservative.
Fedora serves as upstream for future versions
of RHEL. RHEL trees are forked off the Fedora
repository, and released after a substantial
stabilization and quality assurance effort.
For example, RHEL 6 was forked from Fedora
at the end of 2009 and released more or less
together with Fedora 14. By the time RHEL
6 was released, many features from Fedora
13 and 14 had already been backported into
it. The Fedora Project lists the following
lineages for older Red Hat Enterprise releases:
Red Hat Linux 6.2/7 → Red Hat Linux Enterprise
Edition 6.2E
Red Hat Linux 7.2 → Red Hat Enterprise Linux
2.1
Red Hat Linux 10 beta 1 → Red Hat Enterprise
Linux 3
Fedora Core 3 → Red Hat Enterprise Linux
4
Fedora Core 6 → Red Hat Enterprise Linux
5
Fedora 12, 13 → Red Hat Enterprise Linux
6
Fedora 19 → Red Hat Enterprise Linux 7
(Note about Fedora Core 1 and Red Hat Enterprise
Linux 3: Red Hat released Red Hat Linux 10
beta 1, then took two forks from that codebase
to seed both Fedora Core 1 and Red Hat Enterprise
Linux 3 beta releases. There was some cross-pollination
between the two up until shortly before the
first production RHEL 3 release. Therefore,
both FC1 and RHEL3 came from a common fork
of RHL10beta1.)
In addition, the Fedora project includes Extra
Packages for Enterprise Linux, a community-provided
set of packages for RHEL going beyond the
ones that Red Hat selected for inclusion in
its supported distribution.
“Both Fedora and Red Hat Enterprise Linux
are open source. Fedora is a free distribution
and community project and upstream for Red
Hat Enterprise Linux. Fedora is a general
purpose system that gives Red Hat and the
rest of its contributor community the chance
to innovate rapidly with new technologies.
Red Hat Enterprise Linux is a commercial enterprise
operating system and has its own set of test
phases including alpha and beta releases which
are separate and distinct from Fedora development.”
Rebuilds
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. The use of trademarks prevents verbatim
copying of Red Hat Enterprise Linux.
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 include CentOS, Oracle
Linux, Scientific Linux, White Box Enterprise
Linux, StartCom Enterprise Linux, Pie Box
Enterprise Linux, X/OS, Lineox, and Bull's
XBAS for high-performance computing. All provide
a free mechanism for applying updates without
paying a service fee to the distributor.
Rebuilds of Red Hat Enterprise Linux are free
but do not get any commercial support or consulting
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.
Unusually, Red Hat took steps to obfuscate
their changes to the Linux kernel for 6.0
by not publicly providing the patch files
for their changes in the source tarball, and
only releasing the finished product in source
form. Speculation suggested that the move
was made to affect Oracle's competing rebuild
and support services, which further modifies
the distribution. This practice however, still
complies with the GNU GPL since source code
is defined as "[the] preferred form of the
work for making modifications to it", and
the distribution still complies with this
definition. Red Hat's CTO Brian Stevens later
confirmed the change, stating that certain
information would now only be provided to
paying customers to make the Red Hat product
more competitive against the growing number
of companies offering support for products
based on RHEL. CentOS developers had no objections
to the change since they do not make any changes
to the kernel beyond what is provided by Red
Hat.
Commercial products
A number of commercial vendors use Red Hat
Enterprise Linux as a base for the operating
system in their products. Two of the best
known are the Console Operating System in
VMware ESX Server and Oracle Linux respin.
Version history
RHEL 2.1
Red Hat Enterprise Linux 2.1 AS, 26 March
2002. Uses Linux 2.4.9-e.3Update 1, 14 February
2003
Update 2, 29 May 2003
Update 3, 19 December 2003
Update 4, 21 April 2004
Update 5, 18 August 2004
Update 6, 13 December 2004
Update 7, 28 April 2005
Red Hat Enterprise Linux 2.1 ES, May 2003
RHEL 3
Red Hat Enterprise Linux 3, 22 October 2003.
Uses Linux 2.4.21-4Update 1, 16 January 2004
Update 2, 12 May 2004
Update 3, 3 September 2004
Update 4, 12 December 2004
Update 5, 18 May 2005
Update 6, 28 September 2005
Update 7, 17 March 2006
Update 8, 20 July 2006
Update 9, 15 June 2007
RHEL 4
Red Hat Enterprise Linux 4, 15 February 2005.
Uses Linux kernel 2.6.9-54.1, also termed
Update 1, 8 June 2005
4.2, also termed Update 2, 5 October 2005
4.3, also termed Update 3, 12 March 2006
4.4, also termed Update 4, 10 August 2006
4.5, also termed Update 5, 1 May 2007
4.6, also termed Update 6, 15 November 2007
4.7, also termed Update 7, 29 July 2008
4.8, also termed Update 8, 19 May 2009
4.9, also termed Update 9, 16 February 2011
RHEL 5
Red Hat Enterprise Linux 5, 14 March 2007.
Uses Linux kernel 2.6.18-85.1, also termed
Update 1, 7 November 2007
5.2, also termed Update 2, 21 May 2008
5.3, also termed Update 3, 20 January 2009
5.4, also termed Update 4, 2 September 2009
5.5, also termed Update 5, 30 March 2010
5.6, also termed Update 6, 13 January 2011
5.7, also termed Update 7, 21 July 2011
5.8, also termed Update 8, 20 February 2012
5.9, also termed Update 9, 7 January 2013
5.10, also termed Update 10, 1 October 2013
RHEL 6
Red Hat Enterprise Linux 6 was forked from
Fedora 12 and contains many backported features
from Fedora 13 and 14.
Red Hat Enterprise Linux 6, 10 November 2010
Uses Linux kernel 2.6.32-716.1, also termed
Update 1, 19 May 2011
6.2, also termed Update 2, 6 December 2011
6.3, also termed Update 3, 20 June 2012
6.4, also termed Update 4, 21 February 2013
6.5, also termed Update 5, 21 November 2013
RHEL 7
Red Hat Enterprise Linux 7 is based on Fedora
19 and upstream Linux kernel 3.10. The first
beta was announced on 11 December 2013, and
a release candidate was made available on
15 April 2014. On 10 June 2014 Red Hat Enterprise
Linux 7 was officially released.
Red Hat Enterprise Linux 7.0, 10 June 2014
Uses Linux kernel 3.10.0-123
Product life cycle
The life cycle of Red Hat Enterprise Linux
is 10 years for versions 3 and 4, while it
spans 13 years for more recent versions 5,
6 and 7. The life cycle comprises several
phases of varying length with varying degrees
of support. During the first phase, Red Hat
provides full support and updates software
and hardware drivers. In later phases only
security fixes are provided and support for
new hardware is gradually reduced.
In the last three years of the life cycle
critical and security-related fixes are only
provided to customers who pay an additional
subscription which is available for RHEL3/4
only and covers a limited number of packages.
References
Further reading
Jang, Michael H.. RHCE Red Hat Certified Engineer
Linux Study Guide. New York: McGraw-Hill.
ISBN 978-0-07-226454-8. 
Ghori, Asghar. Red Hat Certified Technician
& Engineer. Reston: Global Village Publishing.
ISBN 978-1-61584-430-2. 
Fox, Tammy. Red Hat Enterprise Linux 5 Administration
Unleashed. Indianapolis, Ind.: Sams. ISBN 978-0-672-32892-3.
OCLC 137291425. 
McCarty, Bill. Learning Red Hat Enterprise
Linux 
and Fedora. Sebastopol, CA: O'Reilly. ISBN 978-0-596-00589-4.
OCLC 55130915. 
Negus, Christopher. Fedora 9 and Red 
Hat Enterprise Linux Bible. Indianapolis,
Ind.: Wiley. ISBN 978-0-470-37362-0. OCLC 222155845. 
Sobell, Mark G.. Practical Guide to Fedora
and Red Hat Enterprise Linux. Upper Saddle
River, NJ: Prentice Hall. ISBN 978-0-13-714295-8.
OCLC 216616647. 
Collings, Terry. Red Hat 
Enterprise Linux 4 For Dummies. Hoboken, N.J.:
Wiley. ISBN 978-0-7645-7713-0. OCLC 58973830. 
Petersen, Richard. Red Hat Enterprise Linux
& Fedora Core 4: The Complete Reference. London:
McGraw-Hill. ISBN 978-0-07-226154-7. OCLC 62293551. 
External links
Official website
Brian Stevens, CTO and vice president of engineering,
Red Hat on why Red Hat Enterprise Linux is
"The Business OS for Flexibility and Value"
Red Hat Enterprise Linux at DistroWatch
