The company, which sponsors the Ubuntu Linux distribution, has run a scheme called ShipIt for the past five years which sends free Ubuntu CDs to anyone who wants one. But Canonical is now limiting the CDs to one per person owing to high demand.
"While these CDs are often referred to as 'free' they are, of course, not free of cost to Canonical," said Canonical chief operating officer Jane Silber in a blog post.
"We want to continue this programme, but Ubuntu's growth means that some changes are necessary. Therefore we are adjusting how we handle CD requests to try to find the right balance between availability of CDs and the continued viability of the ShipIt programme."
People will still be able to order the CDs, Silber said, but upgrades will have to be downloaded once the user has installed the operating system. This will not apply to those who have contributed code to the Ubuntu library.
The goal is to get more CDs to people with poor access to downloads, according to Silber. Ubuntu is particularly strong in Africa and South America, and Canonical is trying to maintain and nurture these markets.
People with fast data connections can simply download the software directly, or in an ISO format that can be burned onto a CD and run in that way.