Red Hat Enterprise Linux/zh-cn

Red Hat Enterprise Linux (or RHEL) is a commercially supported derivative of Fedora tailored to meet the requirements of enterprise customers. It is a commercial product from Red Hat which also sponsors Fedora as a community project. Fedora is upstream for Red Hat Enterprise Linux but there are several other Derived distributions available too.

What's the difference between Fedora and Red Hat Enterprise Linux?
Watch a video from Red Hat Magazine.

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 releaes which are separate and distinct from Fedora development.

The cost of Red Hat Enterprise Linux comes from the subscription, which provides assorted certifications and support for additional architectures, as well as 7 years and more of enterprise support. Red Hat also enhances its Red Hat Enterprise Linux offerings with additional software and with certification programs.

More information on the release history and lineage is available at History of Red Hat Linux.

When you purchase Red Hat Enterprise Linux, you are also helping to support Fedora. Since Red Hat sponsors Fedora, what is good for Red Hat is usually good for Fedora. The major differences are:


 * Support and associated services: Red Hat Enterprise Linux is a commercially supported product by Red Hat and provides service level agreements that is important for enterprise customers. This support involves both product assistance (hand holding) as well as prioritization of bug fixes and feature requests, certified hardware and software among other things. Fedora is supported by a wide community of developers and users but it is not commercially supported by Red Hat. Red Hat does sponsor a large number of resources and  funds  to the Fedora project including engineering, marketing and other services.


 * Lifecycle: A new version of Red Hat Enterprise Linux comes out every few years and is supported for up to 7 years and can even be extended to 10 years or more with additional subscriptions. New Fedora releases are available about every six months and every release gets updates for about 13 months.


 * Software Packages: Software in Red Hat Enterprise Linux is a limited subset of Fedora and has about 4000 binary packages (RHEL 6). These are the ones enterprise customers demand and are supported by Red Hat. Fedora offers a wide range of software packages and the latest release has well over 25000 unique (not counting updates in Fedora 15) binary software packages available in the repository.


 * Software Updates: Post release updates of software in Red Hat Enterprise Linux are usually limited to backported security and bug fixes, although enhancements are also offered usually via the major scheduled updates. Red Hat also offers extended update support for customers wishing to stick to a single point release for a longer amount of time. Red Hat also aims to provide ABI compatibility within a release, whereas this is not guaranteed by the Fedora Project. Fedora software packages and updates are close to  upstream and include new features routinely.


 * New Releases: Subscriptions are for a specified time period and not for a particular release. So you can move to any currently supported release of Red Hat Enterprise Linux including new versions of RHEL

Red Hat has a page explaining the benefits of the subscription in more detail. It also provides an older comparison between the two options.

What about packages not part of Red Hat Enterprise Linux? What is EPEL?
In order to focus Red Hat's efforts and limit support costs, only a selected subset of packages found in Fedora are included in the commercially supported product line. The Fedora Project has a community of people maintaining add-on packages for Red Hat Enterprise Linux and compatible rebuilds called Extra Packages for Enterprise Linux, or EPEL.

What is the release cycle of Red Hat Enterprise Linux?
There is no fixed release schedule for new releases. Red Hat Enterprise Linux is usually released approximately every 18 to 36 months and each release is maintained for 7 years and can be extended up to 10 years. Red Hat also offers extended update support for customers wishing to stick to a single point release for a longer amount of time.

What is the update policy for Red Hat Enterprise Linux?
Red Hat Enterprise Linux updates are more conservative and generally focus on security and bug fixes. Hardware enablement and targeted enhancements are delivered via scheduled minor updates and the policy is described in much more detail here

Fedora's Updates_Policy is more liberal compared to Red Hat Enterprise Linux.

Is Red Hat Enterprise Linux available for free or low cost?
It is a commercial product and not available for free. There is a evaluation version for free download at https://www.redhat.com/rhel/details/eval/ and a version with JBoss and Eclipse bundled for 99$ at

http://www.redhat.com/developer_studio/

Academic editions are available at a low cost

http://www.redhat.com/solutions/education/academic/

http://www.redhat.com/solutions/education/academic/individual/

Is Red Hat Enterprise Linux a open source product?
Yes. Binaries and updates are part of the commercial subscription from Red Hat to its customers. The complete source code in the form of source RPM's is available publicly at Red Hat's ftp mirror, which is above and beyond the requirements of any of the free and open source licenses. Red Hat also provides a complementary repository containing small number of additional packages which are licensed from its partners under different licensing terms.

Is it possible to use the publicly available source RPMs to rebuild the distribution?
Absolutely. All the SRPMS are under free and open source licenses that permit this. There are several such rebuilds and derivatives of Red Hat Enterprise Linux available. CentOS and Scientific Linux are popular ones.

What's the difference between rebuilds and Red Hat Enterprise Linux ?
Red Hat Enterprise Linux is commercially supported by Red Hat, and offers a range of software and hardware certifications including third party ISV applications. Rebuilds often have a substantial delay in releasing updates and especially for releasing rebuilds for major releases of RHEL or minor point updates following that. Red Hat also offers other management features via a web service called Red Hat Network that is not available to such rebuilds. Also, layered products such as Red Hat Application Stack, Red Hat Directory Server and Red Hat Satellite are only supported on top of Red Hat Enterprise Linux subscriptions. Many hardware, software and security certifications are only valid on Red Hat Enterprise Linux and not the rebuilds. Much of the technical content of Red Hat knowledge base and customer support portal is only available to Red Hat customers as well.

What's the relationship between rebuilds and Red Hat?
There is no official relationship, but it is a complementary one for which Red Hat has publicly expressed its support, since many of the users using such rebuilds become Red Hat customers when they move into production deployments requiring commercial backing and support.

Red Hat has gone out of its way to make it easier for rebuilds by isolating the Red Hat branding to a couple of specific packages and providing all the source RPM packages in a public location.

History
Red Hat first offered an enterprise Linux support subscription for Red Hat Linux 6.1. It was not a separate product but the subscription level was branded as Red Hat 6.2E. Subsequently, Red Hat started creating a separate product with commercial service level agreements and longer lifecyle based on Red Hat Linux and later on Fedora. This was initially called as Advanced Server and rebranded as Red Hat Enterprise Linux in 2003. The following table gives the lineage:

Articles

 * http://www.redhat.com/magazine/019may06/features/fedora_rhel_1/
 * http://www.redhat.com/magazine/020jun06/features/fedora_rhel_2/
 * http://www.redhat.com/magazine/021jul06/features/fedora_rhel_3/
 * http://www.redhat.com/magazine/022aug06/features/fedora_rhel_4/