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 Cent OS, Oracle Linux, Scientific Linux, White Box Enterprise Linux, Start Com Enterprise Linux, Pie Box Enterprise Linux, X/OS, Lineox, and Bull's XBAS for high-performance computing.
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: (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.
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.
It was based on Red Hat Linux, but used a much more conservative release cycle.
Developers need to register for the Red Hat Developer Program and agree to licensing terms forbidding production use.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 (approximately at the time of the Fedora 12 release) and released more or less together with Fedora 14.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.
Red Hat Enterprise Linux release schedules do not follow that of Fedora (around 6 months per release) but are more conservative (2 years or more).