At last count, there are something like 300 flavors of Linux, and pretty much any of these can be put into service as servers. Indeed, in Linux's early days, nearly all distributions were "all purpose" distros, but it didn't take long for specialization to give rise to dedicated Linux server distributions, and by the early 21st century, every company trying to monetize Linux was offering a server edition.
Contrary to some beliefs, Linux distros are rarely just carbon copies of other distros. As is evident in this look at five of the most popular Linux server distributions, each is different, with distinct strengths and weaknesses.
Red Hat Enterprise Linux
Red Hat's flagship offering tops this list mainly because this year the company is set to become a $4 billion enterprise in annual revenue and because even though it's no longer a Linux-only company, everything it does is still built on its Linux operating system. But even before Red Hat set its sights on the hybrid cloud, RHEL was the go-to flavor of Linux for the enterprise because of the perception that it's rock solid, both in terms of security and reliability.
The $4 billion a year part is important too. Red Hat is by far the strongest financially of the pure open source players, giving the company capital to spend on research and development in order to stay ahead of the curve. It also means the company isn't likely to go away anytime soon, and enterprise customers depend on stability.
We can pretty much guesstimate that Ubuntu is the most used Linux server distribution in the cloud just by taking a quick look at the distro's numbers on Amazon Web Services. These days, according to The Cloud Market, any time you look you're likely to see over 200,000 instances of Ubuntu spun up on EC2, followed by less than 90,000 for Amazon's own homegrown version of Linux or less than 20,000 for Red Hat.
Don't jump to any conclusions over these numbers, however. Although support contracts for Ubuntu are available, it can be spun up for free and without a contract, while the Linux server distributions Red Hat and SUSE require costly support contracts. Even so, the numbers are still impressive, and there are sure to be more than a few on-premises servers running Ubuntu just because that's what the company has running in the cloud too.
Ubuntu's success as a Linux server distribution is pretty impressive, considering that Ubuntu is a relative newcomer to the server game. Born in the first decade of the current century, the distribution bats against established names which have been around since Linux's early years. These days it brings much more to the table than a zero dollar price tag. For example, during the last year or so it's been gaining traction with Snap, it's universal Linux packages which makes installing software a...well, snap. Meanwhile, Red Hat is pushing a similar feature called Flatpak.
OK, this distro pretty much is a carbon copy -- of RHEL. But with its first release in 2004 it had an immediate impact on the server world.
Before then most shared hosting companies built their Linux offerings on Red Hat. That changed almost overnight with the introduction of CentOS. Why? Because it's basically a clone of RHEL, and it doesn't require a support contract. This was very attractive to hosting companies that didn't really need outside support as they had support folks who understood Linux on their payrolls. This made CentOS a great way to cut costs.
In 2014, Red Hat took the distro under it's wings, and it now owns the trademarks and employs nearly all of its lead developers. Officially, the distro remains independent, governed by an independent board, and its Red Hat employees work for Red Hat's Open Source and Standards team and not RHEL. Because of the Red Hat connection, however, CentOS receives the same patches as RHEL, but on a slightly delayed basis. For those not wanting to go it alone, support is available for CentOS from a number of third party vendors.
SUSE Linux Enterprise Server
SUSE, a Germany-based distrubution, has been around since 1992 and predates both Red Hat and Debian by a year. Until it was bought by Novell in 2003, SUSE was considered to be something of a crown jewel of Linux distributions, primarily due to its administrative and maintenance tool, YaSP, which was considered best-of-breed. Under Novell, its reputation went south quickly, especially among open source advocates, largely due to a partnership Novell brokered with Microsoft that many thought violated the terms of the Linux license since it absolved SUSE users for infringing any of the Linux related patents Redmond claimed to own.
These days SUSE operates as a semi-autonomous business unit of Micro Focus, the company that eventually ended up with Novell's assets, and is on something of a comeback. With everybody from Red Hat to Ubuntu partnering with Microsoft, many open source advocates have either forgotten or forgiven SUSE's long ago relationship with Microsoft. Last year SUSE took control of what had been Hewlett Packard Enterprise's implementation of OpenStack and Cloud Foundry, and HPE named the distro its "preferred open source partner" for those two projects as well as Linux.
You might be excused for wondering what a community-based desktop distro known for its free software policies and developed by a nonprofit organization called Software in the Public Interest is doing on a list of Linux server distros. The fact is that the distro has always been extremely popular as a server operating system, and depending on who you read, either Debian or CentOS takes the lead for powering the most websites. If you start counting Debian's derivatives, CentOS isn't even in the race, since a host of other Linux distros, including Ubuntu, are based on Debian.
Although Debian perhaps doesn't have the polish associated with many distributions, it's still considered by many Linux users to be the standard by which other distros are measured. Indeed, on DistroWatch's Page Hit Ranking -- unscientific but as close as Linux gets to having a Hot 100 distribution chart -- the distro currently has a third place ranking. As a server, Debian's "stable" edition is reliable to a fault (some, including some downstream distros, think it too conservative and opt for the "unstable" branch).