Upstream Testbeds and Downstream Forks of RHEL

Red Hat Enterprise Linux (RHEL) is a popular Linux distribution used by many engineers and enterprises worldwide. It provides a stable and reliable platform for enterprise environments, with long-term support (LTS) cycles that can last up to 10 years. There are also several upstream testbeds and downstream forks of RHEL that provide similar functionality and features.

  • Upstream testbeds are community-driven distributions that serve as testing grounds for new features and technologies that may eventually make their way into RHEL.
  • Downstream forks, on the other hand, are typically designed to be as close to 1:1 binary compatible with RHEL as possible, there may be some small differences between the two distributions.

Understanding the differences between these upstream testbeds and downstream forks is essential to choose the right distribution for their needs. In this post, we will explore them.  

Upstream Testbeds


Fedora is a community-driven Linux distribution sponsored by Red Hat, Inc. and is known for its cutting-edge features and rapid development cycle. The distribution was initially released in 2003 as Fedora Core, and was created by Warren Togami, Michael K. Johnson, and Seth Vidal. The distribution is maintained by the Fedora Project, which is composed of both Red Hat employees and community volunteers. Fedora has a short release cycle of approximately 6 months, which allows for rapid iteration and the inclusion of new features and technologies. Fedora has gained popularity among developers and Linux enthusiasts for its focus on innovation and bleeding-edge technology, including the Btrfs file system, the latest versions of the Linux kernel, GNOME desktop environment, and other key software components. According to the latest usage statistics, Fedora is the 5th most popular Linux distribution in terms of web traffic and the 4th most popular distribution among Linux developers.

CentOS Stream

CentOS Stream is a rolling-release Linux distribution that was introduced by Red Hat in December 2020 as a replacement for CentOS Linux. The project is led by Brian Exelbierd, a former Red Hat employee, and is designed to serve as an upstream testbed for RHEL, providing early access to new features and technologies. Unlike CentOS Linux, which provided a stable, fixed-release OS, CentOS Stream provides a more dynamic, constantly evolving OS that is updated frequently. This approach allows developers and engineers to test and experiment with new features and technologies before they are released in RHEL. However, the end of support for CentOS Linux has led to some controversy, with some users expressing disappointment and frustration with the shift to CentOS Stream.  

Downstream Forks

Scientific Linux (Discontinued)

Scientific Linux was initially created by Fermi National Accelerator Laboratory (Fermilab), a U.S. Department of Energy particle physics and accelerator laboratory located in Batavia, llinois in 2004. Fermilab created Scientific Linux as a way to provide a stable and consistent platform for scientific computing, with a focus on the needs of high-energy physics experiments. Scientific Linux was based on Red Hat Enterprise Linux and was binary-compatible with RHEL, meaning that it can use the same packages and software repositories as RHEL. This made it easy for users of RHEL to switch to Scientific Linux without having to learn a new operating system. Over the years, Scientific Linux had gained a strong following in the scientific research community, with many organizations and institutions using it as their primary operating system for scientific computing. In addition to Fermilab, Scientific Linux was also maintained by a consortium of scientific organizations, including CERN, DESY, and SLAC. However, with the announcement that Fermilab will no longer be maintaining the distribution, many users are now looking for alternative distributions to replace Scientific Linux.

Fermi Linux

Fermi Linux is designed for use in scientific research environments and is maintained by the Fermilab, Fermi Linux was first released in 2004. It is optimized for high-performance computing and includes support for OpenMPI and other parallel processing frameworks. While Fermi Linux is not as widely used as other downstream forks of RHEL, such as CentOS Linux and Scientific Linux, it has a dedicated user base in the scientific research community.

CentOS Linux (Discontinued)

CentOS Linux was a popular downstream fork of RHEL that was created in 2004 by a group of open-source developers led by Gregory Kurtzer, CentOS Linux aimed to provide a stable, and community-driven alternative to RHEL. It gained high popularity among enterprises that wanted to use RHEL without paying for commercial support. CentOS Linux was compatible with RHEL and used the same source code to build its packages, ensuring a 1:1 binary compatibility with RHEL. This made it easy for users to switch between RHEL and CentOS Linux without encountering compatibility issues. CentOS Linux was widely used in a variety of applications, including web servers, databases, cloud computing, and scientific research. It was also used as a development platform for software projects, as it provided a stable and consistent environment for building and testing software. According to some estimates, CentOS Linux was among the top 5 Linux distributions used in enterprise environments. Despite its popularity, in 2020, Red Hat, Inc. announced that it was ending support for CentOS Linux 8, which was expected to be the last version of CentOS Linux.

Oracle Linux

Oracle Linux was introduced in 2006 by Oracle Corporation, a multinational technology company based in the United States. The distribution is based on RHEL and is designed to be compatible with RHEL packages and drivers, making it an attractive choice for enterprises that want to run Oracle software on a Linux OS. Oracle Linux was created after Oracle Corporation acquired the software company, Unbreakable Linux, which was focused on providing support for RHEL at a lower cost. The acquisition allowed Oracle to enter the Linux market and offer its own Linux distribution, while also providing support for RHEL. Oracle Linux offers both free and paid versions of the distribution. The free version, known as Oracle Linux for developers, is designed for non-production use and provides access to all of the same packages and updates as the paid version. The paid version, known as Oracle Linux Premier Support, offers enterprise-level support and additional features such as access to Ksplice, a tool that allows for in-memory patching of the Linux kernel. According to the 2021 Linux Foundation’s Enterprise End User Report, Oracle Linux is used by around 10% of enterprises surveyed, making it the fifth most popular Linux distribution for enterprise use. The distribution is particularly popular in industries such as financial services, healthcare, and retail, where enterprises have a significant investment in Oracle software.


AlmaLinux is a enterprise-grade distribution that was created as a replacement for CentOS Linux after the announcement of CentOS Stream. AlmaLinux was created by the team behind CloudLinux, Inc., a company that specializes in providing secure and stable Linux hosting environments. The development of AlmaLinux was led by Igor Seletskiy, the CEO of CloudLinux. Now, it is maintained by the AlmaLinux Foundation. The first stable release of AlmaLinux was made available in March 2021, and it was met with enthusiasm from the Linux community. The project quickly gained popularity worldwide. AlmaLinux provides a 1:1 binary compatibility with RHEL, meaning that it is designed to be fully compatible with RHEL without requiring any additional modifications or software. This makes it an attractive choice for enterprises that require a stable, long-term supported operating system that is compatible with RHEL, but without the need for commercial support. According to the AlmaLinux website, the distribution has been downloaded over 700,000 times since its launch, and it has been adopted by many enterprises worldwide, including GoDaddy, Siemens, and Cloudflare.

Rocky Linux

Rocky Linux is a community-driven replacement for the recently discontinued CentOS Linux. It was announced by Gregory Kurtzer, the founder of CentOS Linux, in December 2020, soon after the news of CentOS’s shift in focus to CentOS Stream. Rocky Linux aims to be a 1:1 binary-compatible downstream fork of RHEL, just like CentOS Linux was. Its development is community-driven, and it is sponsored by the Rocky Enterprise Software Foundation (RESF), a non-profit organization formed to ensure the long-term development and stability of the project. As of April 2023, Rocky Linux is gaining popularity among the Linux community, with over 1.5 million downloads since its initial release in June 2021. Its popularity is largely due to its community-driven development model and non-profit sponsorship by the RESF provide assurance of its longevity and stability.


ClearOS is developed and maintained by ClearCenter, a Utah, USA. ClearOS was initially released in 2009, and it is based on CentOS, just like many other downstream forks of RHEL. ClearOS is designed to be a simple, easy-to-use operating system that includes all the necessary features for small business networks, such as a web-based Graphical User Interface (GUI), file and print services, mail server, web server, and firewall. It also includes additional features such as VPN, intrusion detection, and anti-virus and anti-spam filters. In addition to the free community version, ClearCenter also offers a paid version of ClearOS that includes additional features and support. According to the ClearCenter website, ClearOS has been downloaded over 430,000 times, and it has over 400,000 deployments worldwide.  


Have you used any of the upstream testbeds or downstream forks of RHEL before? If so, which one did you prefer and why? Understanding the different options available can help you make an informed decision when choosing the right Linux distribution for your needs.  


Abdullah As-Sadeed

Abdullah As-Sadeed