I heard that Ubuntu is not completely free (as in Freedom). What are the specific parts of Ubuntu that are not Free?
Assuming you mean "Free as in Freedom" rather than "free as in beer" (see this essay for one description of the difference between the two), a person claiming that Ubuntu is not free may be referring to one of the following issues:
- Binary blobs in the Linux kernel (this is often firmware that is needed to let a free driver work).
- Non-free hardware drivers.
- Non-free software that is in the Ubuntu repositories, such as flash.
Sometimes, they may be referring to the inclusion of software that poses legal problems in the US because of patents or other issues; however, such issues are usually orthogonal to the software being free.
However, it is more than possible to have a completely free system using Ubuntu. The
vrms package in the Ubuntu repository is a good first step if you are concerned with non-free packages that are installed on your system. If you want to go even further, you can consider using Linux Libre a version of the Linux kernel that has non-free binary blobs removed from it. Note, however, that installing linux libre will break your support for any hardware that needs those non-free bits.
I personally find it "free enough" to ensure that I don't have any non-free packages installed and tend not to worry about binary blobs. But each person tends to draw "the freedom line" in a different place.
For one thing, it uses closed source hardware drivers, which aren't regarded "free" the GNU way. That's one of the reasons, why some drivers aren't supported on Fedora. There's different kinds of "free" in the Linux world. Closed source is what makes a Distro not GPLv2 compatible, which clearly requires addition of all the source codes.
Ubuntu provides specific repositories of nonfree software, and Canonical expressly promotes and recommends nonfree software under the Ubuntu name in some of their distribution channels. Ubuntu offers the option to install only free packages, which means it also offers the option to install nonfree packages too. In addition, the version of Linux, the kernel, included in Ubuntu contains firmware blobs.
As of October 2012, Ubuntu sends personal data about users' searches to a server belonging to Canonical, which sends back ads to buy things from Amazon. This does not, strictly speaking, affect whether Ubuntu is free software, but it is a violation of users' privacy. It also encourages buying from Amazon, a company associated with DRM as well as mistreatment of workers, authors and publishers.
This adware is one of the rare occasions in which a free software developer persists in keeping a malicious feature in its version of a program.
Ubuntu appears to permit commercial redistribution of exact copies with the trademarks; removal of the trademarks is required only for modified versions. That is an acceptable policy for trademarks. The same page, further down, makes a vague and ominous statement about “Ubuntu patents,” without giving enough details to show whether that constitutes aggression or not.
That page spreads confusion by using the misleading term "intellectual property rights", which falsely presumes that trademark law and patent law and several other laws belong in one single conceptual framework. Use of that term is harmful, without exception, so after making a reference to someone else's use of the term, we should always reject it. However, that is not a substantive issue about Ubuntu as a GNU/Linux distribution.