Debian and Ubuntu are the most influential Linux distributions ever. Of the 285 active distributions listed on Distrowatch, 132 are derived from Debian, including Ubuntu, and another 67 are derived directly from Ubuntu -- just under 70%. Yet the experience of using them differs in just about every aspect. Consequently, choosing between them is no easy matter.
Asked to explain the difference between the two distributions, most users would describe Debian as an expert's distribution, and Ubuntu as a beginner's. These characterizations are partly true, but exaggerated. Debian's reputation rests on its state over a decade ago, and today allows as much hands-on control as each user chooses.
Similarly, Ubuntu is really its design team's conception of easy. Should your work habits not be compatible with that concept, you may disagree strongly that it is easy to use.
However, although Ubuntu is derived from Debian, their differences are marked. From installation and desktop to package management and community, what everybody thinks they know about the two may be wrong, or at least in need of heavy qualification -- all of which makes choosing which is right for you a difficult process.
Right away, the distribution for you may depend on your hardware. Debian currently develops for 13 hardware architectures, ranging from standard 32 and 64 bit Intel to Arm and PowerPC, with support for two more in progress. By contrast, Ubuntu supports 32 and 64 bit versions as computer desktop environments, and is developing Ubuntu ARM for mobile devices.
Another consideration is the installers for each distribution. Ubuntu's standard installer is designed to require a minimum of user input to keep installation simple and as fast as possible. Should you encounter problems, you can try the expert mode installer -- a lightly re-branded version of the Debian Installer.
The Debian Installer clearly has other priorities. Its graphic version is a GUI that differs from the text-based installer mainly in toolkit, offering no advantage except comfort for those nervous about the command line.
Contrary to Debian's former reputation, it can usually be installed by following the online instructions and accepting the default settings for each stage. However, if you choose, you can make individual choices at every step of the installation process, substantially increasing the required time. Instead of catering to inexperienced users, the Debian installer accommodates all levels of users. It may not be pretty, but, short of compiling your own packages, you are unlikely to find a more flexible installer.
Debian and Ubuntu default to different desktop environments. Ubuntu defaults to Unity, the desktop that Canonical, Ubuntu's corporate sponsor, has been developing for the last five years. Should Canonical succeed in marketing its mobile devices, in the future you may be able to have the same desktop on all your hardware.
Debian, though, seems in no hurry to support Unity. Instead, its standard disk images default to GNOME 3.
However, these defaults mean little more than convenience. Both Ubuntu and Debian support multiple desktops. In Ubuntu, other desktops are semi- independent distributions, such as Kubuntu for KDE and Xubuntu for Xfce. These variations share the underlying GNOME technologies with the standard-issue Ubuntu, and may or may not sync with official releases, give or take a few weeks.
In Debian, the choice of desktops is roughly the same, but the teams developing them are less separate from standard Debian. The timeliness of these releases varies, so expect to take some time in online searches to find what is happening with any team whose results may interest you.
Except for Unity, most software written for Ubuntu is also available for Debian. Software written for Debian is almost always available for Ubuntu, because Ubuntu draws its packages from Debian's repositories. Depending on where Debian is in its ponderously slow release cycle, Ubuntu's software is usually more current than Debian's, but as a tradeoff, Debian's tends to be more thoroughly tested and stable.
A warning, though: do not assume that a common origin makes packages cross-compatible. While many packages can be installed on both Debian and Ubuntu, about twenty percent of Ubuntu's packages stand a large chance of being incompatible with Debian due to differences in name and file locations.
Unsurprisingly, both Debian and Ubuntu encourage the use of a root account for administrative purposes, and restricted accounts for everyday computing. However, the chosen security models are different.
In Debian, users do administrative wprl by logging directly into the root account, then -- ideally -- logging out again as quickly as possible to reduce the period of vulnerability. Ubuntu, though, obscures the root password, instead using sudo, and allowing at least one user to enter their own password to issue administrative commands.
Which of these security models is preferable is frequently debated, so you should search for a discussion on the subject so that you can decide which you prefer.
Debian's packages are divided into three main categories: Unstable, Testing, and Stable. A new package enters stable, and transfers into Testing when it has been debugged. When an official release is prepared, the current packages in Testing under further examination, and are eventually become the new Stable.
In recent years, other repositories have been officially or unofficially added, such as Experimental, Old Stable, Security, Backports ,and Update. However, users should pay most attention to the three main repositories.
The advantage of Debian's system is that you can choose a position anywhere between two extremes: rock-solid stability, at the cost of older versions of software, or cutting edge, at the cost of less robust software and, at times, drastic changes in technology that can cripple an unwary user's system. The choice can depend on whether you upgrade a core component, such as the Linux kernel, or a self-contained utility with its own libraries that affects nothing else when disaster strikes.