Introduction
Linux is one of the most popular and powerful operating systems in the world. Thanks to its openness, companies and communities participate in open-source projects around Linux and customize the software to suit their needs. This movement also has led to many Linux distributions.
Each distribution has distinctive features, which enables users to choose the best suited distribution based on their needs. Although there are many, this article will discuss CentOS, an open source OS that has been widely used by enterprises and communities.
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What is CentOS?
CentOS is one of the Linux distributions that are available as open-source. Since its first release in May 2004, it has been widely used in both the community and at an enterprise level thanks to the strengths it provides. It is well known for stability, predictability, and manageability.
The latest version came out in September 2019. Since its inception, CentOS has received great support from the community and has provided its sources to the public by Red Hat. Thus, CentOS is designed to be compatible with RHEL or Red Hat Enterprise Linux.
History of CentOS Versions
As other Linux distros do, CentOS has its own versioning rules and release cycles. Since version 7.0, it started maintaining a minor and a major version. Both version units match those of RHEL. For instance, CentOS 6.3 is made from the packages of RHEL 6 update 3 or RHEL version 6.3.
Also, since version 7.0, CentOS introduced a third part that tells you the month of the source code that it is based upon. For example, version number 7.3-1407 means that it is from RHEL version 7.3 that's based on July 2014.
CentOS Version 8
Version 8 released in September 2019 included a wide range of features and improvements in usability, security, network, and more. To introduce these new features/improvements:
- GNOME session and display manager starts using Wayland as the default display server that provides stronger security and enhanced multi-monitor handling.
- CentOS includes the TCP networking stack version 4.16 which is known for higher performance and reliability.
- The YUM package manager (YUM v4) is available for users to conveniently download and manage packages.
- Version 8 supports Open SSL 1.1.1 and TLS 1.3. It also allows you to protect customer’s data using the latest crypto protection standards.
- It began supporting recent language versions such as Python 3.6, PHP 7.2, Ruby 2.5, Perl 5.26, Node.js, Apache HTTP server 2.4, Nginx 1.14, and more.
CentOS Version 7
Version 7 was released in July 2014. Until the next version 8 came to the market, it provided the following features.
- X.Org (7.7) server was used as the default GNOME Display Manager.
- Version 7 came with an upgraded upstream version 3.18 for the TCP/IP stack that resolved many bugs and achieved enhancements compared to a prior version.
- YUM version 3 was used.
- It started supporting OpenSSL 1.0.1 and TLS 1.0.
- It supported Python 2.7.5, PHP 5.4.16, Ruby 2.0.0, Perl 5.16.3, and more.
CentOS Version 6
CentOS 6 was shown to the market in July 2011. Version 6 is no longer maintained by Red Hat. However, you can still understand how CentOS has evolved over time by learning the features per version.
- X.Org 7.4 server was included as default GNOME Display Manager.
- Version 6 provided support for Python 2.6.6, PHP 5.3.3, Perl 5.10.1, and more.
- YUM version 2 was used.
- It started supporting multi-queue networking, IPv6, Netlabel, wireless networking and devices.
- It supported Python 2.6.6, PHP 5.3.3, Perl 5.10.1, and more.
CentOS Release Cycle
Among these most recent versions of CentOS, version 8 was relatively recent while the other two are old. CentOS has a long support cycle, which is an important factor when you choose a Linux distro. Short support and frequent releases can make maintenance work complicated since users have to mind upgrades and patches. But, CentOS has a long cycle. For example, CentOS 5, 6 and 7 were maintained for 10 years. CentOS was supported for seven years.
The list below shows the release dates since version 3.
| CentOS Version | Release Date | Last Maintenance Updates |
| 3 | 2004-03-19 | 2010-10-31 |
| 4 | 2005-03-09 | 2012-02-29 |
| 5 | 2007-04-12 | 2017-03-31 |
| 6 | 2011-07-10 | 2020-11-30 |
| 7 | 2014-07-07 | 2024-06-30 |
| 8 | 2019-09-24 | 2021-12-31 |
CentOS has been releasing new versions less frequently as it has matured. Recent releases of CentOS tend to be maintained longer.
What is a CentOS Variant
Thanks to strong community support, CentOS is able to have diverse variants. A variant refers to a special edition of CentOS. Each variant is built by replacing or supplementing a specific subset of packages. For example, it can be everything including kernel, networking, and other subsystems.
These variants are mainly created by SIGs or Special Interest Groups. They are groups who are interested in related technologies and hugely contributing to technology in CentOS. The SIGs aim at delivering technology to end users in the easiest way possible.
Versions vs. Variants
You may be confused between versions and variants. A version is used to describe various aspects of the CentOS mainstream, while a variant is a repurposed version of CentOS. You can understand this better by looking at some variant examples.
CentOS Variants
Currently, it is difficult to find an active and largely shared variant. The variants below are not recent but you can still have a look to understand CentOS variants.
- Atomic: The CentOS Atomic provides a minimal image using rpm-ostree, tools, and documentations that help users to create their own CentOS/Atomic images with custom packages.
- Cloud Instance: The CentOS Cloud Instance targets making CentOS cloud instances so that users can easily launch a CentOS instance whether it's on premise or in a cloud environment.
- Xen4CentOS: The Xen4CentOS project helps users to migrate their CentOS-5/Xen infrastructure to CentOS-6, while importing the newer Xen-4 tool sets.
- PaaS: The CentOS PaaS was designed to migrate multiple PaaS stacks into the CentOS ecosystem for users. It allows the stacks to run as a service and to be provided in various formats such as rpms, containers, and images.
Conclusion
CentOS has been proven to be a reliable Linux distribution for enterprise servers and desktops throughout its history. Like other Linux distros, CentOS has its unique versioning and ecosystems. People will certainly benefit from this open-source operating system if they can understand the ins and outs of CentOS. However, that can be challenging if you are not familiar with a Linux system.
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