We recently reviewed the Top 5 Linux distributions for 2012 focusing on desktop (workstation) tailored distributions. But if there is an area where Linux is a king, this is certainly the server area. The internet is at this point populated by servers running Linux that a word was created for them: LAMP, designing the most used software association on these servers ( Linux Apache MySQL PHP ). The popularity of these Linux servers is not only due to their low cost, but also to their stability — most have not been rebooted in years.
What usually makes a Linux server oriented distribution different to its workstation counterpart is long term support, focus on stability of offered packages, as well as optimization of network performances.
Red Hat Enterprise Linux
Red Hat Enterprise Linux is, as you could guess, a server distribution commercially supported by Red Hat. Being enterprise oriented, this distribution is aiming to suit the needs of medium to big enterprises. Red hat Enterprise Linux comes with long term support (at least 7 years) , is optimized for multicored systems, and supports a large variety of hardware.
CentOS / ClearOS
If the subscription costs of Red Hat Enterprise Linux support, ranging from few hundred dollars to thousands, can be an insurmountable obstacle for small business or independent entrepreneur, there are fortunately similar distributions available.
CentOS is without doubt the most known of these free alternatives. Being 100% binary compatible, frequently updated, and supported by a large user community, it is an obvious choice.
ClearOS is a little more than a free alternative, providing unique features, like cloud connection and an easy to use web-based administration interface. In addition to a free community edition, ClearOS also offers a professional edition.
Ubuntu / Debian
As there are Red Hat based Linux distribution, there are Debian based ones, Ubuntu Server Edition being one of the most popular.
A nice thing about Debian based Linux servers is that you never need to install a new distribution, as their package manager lets you upgrade your system easily and indefinitely.