Ubuntu, which is more inclined to be a OS for desktops is gaining more popularity as a server OS. Lately, statistics done by W3Techs show that Ubuntu is installed on 7% of servers world wide. Thats a huge number given the popularity of the web and more and more websites and servers coming out everyday.
Surprisingly, Red Hat Enterprise Linux, which is mostly a server based OS is installed in just 3.4 percent of servers. Red Hat gains a significant part of revenue from server installations, and the figures should have been more. However, this can be due to the fact that Ubuntu can be obtained for free and has a great community support where as you need to pay to deploy Red Hat Enterprise Linux. Also, Ubuntu has its own version of server OS, Ubuntu server and paid support is available on demand.
Other minor players in this category include Suse and Fedora. Some major players which are mostly targeted at the servers are Debain and CentOS. Debian occupies nearly 32% of all Linux server installations while CentOS has around 27%.