The number of Linux users and installations is impossible to determine. But there are several different statistical information available which can be used to at least get a rough idea of the number of Linux installations world wide.
Merging different statistical data into one number is a tricky exercise and the result is questionable at best. Keep that in mind when you read the following information. The idea is not to get exact numbers but to get a rough idea of the dimension, nothing else.
Source #1: Fedora
One of the best statistical sources regarding Linux usage are the Fedora statistics. There the number of downloaded images as well as the number of unique IPs getting software updates is counted.
The data are difficult to interpret: no one knows if a downloaded image was only used to test the new system or to bun it onto a CD and distribute it to thousands of magazine readers or thousands of company computers. The second number is problematic because one new IP can mean a big NAT network or just a dial-in user who re-connected. So flaws everywhere, but it is a interesting coincidence that the IP numbers and the downloads are rather close.
There are also the smolt data. It tracks the users who opted in to a tracking system. Currently the smolt web server seems to be lacking behind. But there are current data available for older Fedora releases: these informations say that every month Fedora still gets more than 10k new Fedora 7 users – although there are already Fedora 8 and Fedora 9 available.
So the question is how to read all the data. One way was recently suggested by Paul Frields, Fedora’s project leader: he sums up the data to be around 11.5 million. Together with currently 2.5 million Red Hat subscriptions this would result in 13 million users. Focussing on Fedora alone and leaving the Fedora 6 users Fedora would still have a user base of 9.5 million users.
Source #2: relative statistics
There are hardly any other trustfully data from other Linux distributions available. Therefore, the Fedora number does say a lot about Fedora, but not that much about Linux in general. However, there are other statistics which measure the relative acceptance of Linux distributions.
One such source is the 2007 Linux Desktop Survey done by DesktopLinux.com. There the relative importance of Fedora/Red Hat is measured with 9%. Unfortunately there is no more recent survey available. I wonder why no one has picked up such a survey in 2008. Maybe I should start one on my own? :)
Given that Fedora/Red Hat has roughly 10% and also roughly 10 million users together (which in fact seems like a at least slightly realistic data base, given the facts), the total number of Linux users world wide would sum up to 100 million Linux users. Nice.
That would leave Mac OS far behind, which is however not that surprising: Mac OS is hardly used in Offices or the government outside the US, and it is far easier to give Linux a try and keep it as a dual boot option besides a Windows installation. Also, the EU governments are pushing Linux quite a lot, and many companies and governments indeed switch to Linux right now or already switched over in the client space for some of the day-to-day workstations.
Still, last year I played the “numbers game” already (unfortunately with the same relativity source, btw.) and the result said something about 20 to 30 million users. I doubt that the number of Linux users spiked that much in the last year, but think that we can safely say the number of Linux users world wide is somewhere in the middle two digit million area, somewhere around 50 million installations worldwide.
Keep in mind that this counts mainly workstations – not traffic lights, shop information terminals or any other specialized hardware. Including all these devices would result in much, much larger numbers.
The problem: discrepancy
Most numbers available guessing the number of Linux users world wide say that there are not that many Linux installations out there, not at all. Most often it is said that, in percentage, Apple has a low one-digit number, while Linux has a dot before its first non-zero number.
The statistical backup for such numbers is most often created by browser strings aggregated from Web pages. This procedure has the flaw that these strings are often faked to make it easier to access specific pages. Also, the monitored pages are only a subset of the entire web, and surprisingly often focus on the US only which is not representative for the world at any rate.
Still, I do often wonder why such numbers and my estimates are different in the order of magnitudes. I welcome any comment on that issue!