At the Ubuntu Developer Summit (UDS) today in Florida, Ubuntu founder Mark Shuttleworth announced that the Unity shell will become Ubuntu's default user interface across both the desktop and netbook editions. Unity, which was introduced as the new netbook interface in the recent Ubuntu 10.10 release, will arrive on the desktop in Ubuntu 11.04 next year.

Shuttleworth described desktop adoption of Unity as the "most significant change ever" for Ubuntu. He also acknowledged that it is a "risky step" and that much work remains to be done to prepare for the transition. The move reflects Ubuntu's growing divergence from the standard upstream GNOME configuration and effort to differentiate itself with a distinctive user experience. During the keynote, Shuttleworth emphasized that Ubuntu is still committed to GNOME despite the fact that it will ship with Unity instead of GNOME Shell. He contends that diversity and competition between different kinds of GNOME environments will encourage innovation and benefit the GNOME ecosystem.

The decision to ship a custom interface in Ubuntu is going to be controversial. Critics in the upstream community are already expressing disappointment with what they view as a move to fork the desktop. It's worth noting, however, that Canonical isn't the first company to build a unique user experience for GNOME that deviates from the standard upstream user interface stack. Intel also similarly produced a custom shell with the Clutter that is used on the MeeGo platform. Canonical's deviations from the upstream configuration receive closer scrutiny because Ubuntu's popularity among Linux users makes the distribution a king-maker on the Linux desktop. Canonical's decision to ship Unity could deeply marginalize GNOME Shell.

The diverging desktops could pose some challenges for GNOME application developers who will have to support two different sets of desktop integration features. I discussed that issue with Shuttleworth after the keynote to get his perspective. He pointed out that developers are already supporting Ubuntu's indicator system and other custom integration points without much difficulty. He is confident that fragmentation challenges for application developers can be avoided by working through FreeDesktop.org to ensure that desktop integration mechanisms are standardized and interoperable between environments. As an example, he highlighted the collaboration that occurred around the Media Player Remote Interfacing Specification, the protocol that Ubuntu uses to facilitate communication between music players and the desktop's new audio indicator menu in Ubuntu 10.10.

I also asked Shuttleworth why Canonical is building its own shell rather than customizing the GNOME Shell. He says that Canonical made an effort to participate in the GNOME Shell design process and found that Ubuntu's vision for the future of desktop interfaces was fundamentally different from that of the upstream GNOME Shell developers. He says that GNOME's rejection of global menus, for example, is one of the key philosophical differences that would be difficult to reconcile. Canonical has accumulated a team of professional designers with considerable expertise over the past few years. They want to set their own direction and create a user experience that meets the needs of their audience. The other major Linux vendors, who are setting the direction of GNOME Shell's design, have different priorities and are arguably less focused than Ubuntu on serving basic desktop users.

There are also technical issues that drove the decision. Ubuntu's developers are deeply dissatisfied with GNOME's new Mutter window manager, for example, and have decided to use Compiz instead in their Unity environment. Shuttleworth says that Mutter simply couldn't deliver acceptable performance. Shuttleworth also says that Zeitgeist will play an increasingly significant role in Ubuntu even though it is not going to be part of GNOME 3. Zeitgeist is a sophisticated framework that tracks and correlates relationships between the user's activities so that it can supply applications with contextually relevant information to present to users. Zeitgeist was once considered to be a key part of the roadmap for GNOME 3, but was rejected by the upstream community due to cultural differences in its development model. Shuttleworth says that GNOME would benefit from greater receptiveness to outside innovation and is disappointed that the Zeitgeist project isn't being embraced by the upstream community.

Shuttleworth identified multitouch support as a very high priority for Unity. During his keynote, he expressed the belief that multitouch hardware will eventually become ubiquitous in portable computers. The earliest hardware-enablement aspects of Ubuntu's multitouch strategy have already landed in Ubuntu 10.10. Canonical aims to work with application, toolkit, and Xorg developers to bring richer touch interaction to the desktop. He also emphasized the importance of moving beyond the traditional approach to file management. He argued that the "files and folders way of thinking is completely broken" and should be displaced by a more search-centric model and Zeitgeist-enabled tools that rely on context. Despite his enthusiasm for driving innovation in file management, he acknowledged that the file interface in Unity is not sufficiently mature yet. In Ubuntu 11.04, GNOME's traditional Nautilus file manager will be made easily accessible through Unity.

Unity will be at the heart of the ambitious Ubuntu 11.04 roadmap. Due to the enormous magnitude of the changes that it will bring to the Ubuntu desktop, it will likely be a major focus of discussion this week at the Ubuntu Developer Summit. As we concluded in our recent review of Unity, it has considerable potential but still needs a lot of work. During the next six months of Ubuntu development leading up to the 11.04 release, the Ubuntu team will endeavor to make Unity shine.

Listing image by Ryan Paul/Ars Technica