Let's have a pop quiz.

The most popular desktop operating system is... Windows. Right.

The most popular mobile operating system is... Android! Correct.

And, the most popular operating system on the public cloud is... Ubuntu Linux.

Yes, that's right. By The Cloud Market's latest analysis of operating systems on the Amazon Elastic Compute Cloud (EC2), Ubuntu has approximately 135,000 instances. In second place, a long, long way back, you'll find Amazon's own Amazon Linux Amazon Machine Image (AMI), with 54,000. Lagging even farther behind, there's Windows with 17,600 instances. In fourth and fifth place, you'll find CentOS, 8,500, and Red Hat Enterprise Linux (RHEL), 5,600.

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To put this into perspective, by RightScale's latest State of the Cloud report, Amazon Web Services (AWS) dominates the public cloud, with 57 percent of market. Azure Infrastructure-as-a-Service (IaaS) is second with 12 percent. In short, by dominating AWS, Ubuntu is, without doubt, the most popular cloud Linux.

In addition, to AWS, Ubuntu has been available on HP Cloud, and Microsoft Azure since 2013. It's also now available on Google Cloud Platform, Fujitsu, and Joyent.

Canonical, Ubuntu's parent company, is also putting considerable efforts behind OpenStack for the private and hybrid cloud. Indeed, Canonical has also worked with Microsoft to bring Windows Server to OpenStack and with Oracle to bring Oracle Linux to the Ubuntu take on OpenStack.

So, perhaps it should come as no surprise that in the latest OpenStack user survey, Ubuntu dominated OpenStack clouds almost as much as it does the public cloud. Fifty three percent of all production OpenStack clouds are running Ubuntu. CentOS is far in the back with 29 percent.

The fact that Linux so utterly dominates the cloud is no surprise. What many will find surprising is that Ubuntu is on top of the Linux-on-the-cloud mountain.

People still see Ubuntu as primarily a desktop operating system. It's not -- and hasn't been for some time. Ubuntu today is the predominant cloud operating system. The desktop is a nice add-on, but it's not Canonical's focus nor should it be.

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