Mir, Canonical's replacement for the X window system, will not make it into the next version of the Ubuntu desktop.

Canonical initially planned to turn Mir on by default in Ubuntu 13.10, the version shipped in October 2013, but it was dropped due to compatibility problems in multi-monitor setups. It's especially important not to add any buggy technologies to 14.04, the version coming in April 2014, because that is a Long-Term Support (LTS) edition that Canonical must maintain for five years. Mir itself seems to be working fine, but there are problems with XMir, an X11 compatibility layer that ensures Mir can work with applications built for X.

"We will only bring Mir into 14.04 if we can be assured that we're not going to have any support issues," Ubuntu Community Manager Jono Bacon told Ars last month

It now appears Mir won't make it into the next edition. "It was affirmed today that Ubuntu 14.04 LTS will still be shipping with the stable and proven Unity 7 experience, which is designed around using an X.Org Server with Compiz," Phoronix's Michael Larabel wrote today. "It doesn't appear they will try for using XMir by default in this next Long-Term Support release with Unity 7. It was also said today that point releases to Ubuntu 14.04 LTS will not be adding in Mir or Unity 8."

The comments came at the Ubuntu Developer Summit, an online event. Canonical founder Mark Shuttleworth stressed that the 14.04 desktop has to be rock-solid for customers with large-scale deployments, such as educational institutions.

"On the desktop, this will be sort of the crowning release of the Unity 7 code base," he said. "We've been working on that code pretty consistently since round about 10.04, and so we've had four very good years of continuous improvement. We can reasonably expect 14.04 to be a really fast, slick, stable, and reliable release on the desktop. That's the commitment we want to make to anyone who is deploying large volumes of Ubuntu in any large-scale environment."



Shuttleworth was asked whether Mir and Unity 8 will make it into 14.04 in the form of post-release updates and responded as follows:

No. What we'll do with 14.04 is we'll do point releases which introduce support for new hardware at the kernel level and at the X level, but we won't do point releases of 14.04 which introduce Mir and Unity 8. Now, Mir and Unity 8 are in the archive, and they will become, I imagine, more and more useful and usable, and by not making them part of the base release we probably have more flexibility to update them so they may become usable for people. But we certainly will not switch from vanilla X to Mir during the course of the maintenance life of 14.04.

Bacon expanded upon Shuttleworth's remarks in an e-mail to Ars. The goal from the start was to "deliver Mir + XMir + Unity 7 in Ubuntu 14.04 Desktop, and Mir + Unity 8 on the phone and tablet," he wrote.

However, "for the 14.04 Desktop, we are very conscious that this is an LTS release," Bacon continued. "This means that our already fairly conservative assessment of when to land significant new foundational pieces is even more conservative from a quality, technology, and support perspective. We feel that while Mir is on-track (hence its current delivery on the phone and scheduled for tablet too), we have more reservations about quality in terms of the XMir, and we didn't want to risk the LTS experience for our users."

While it won't be enabled by default, adventurous types can still get Mir from the Ubuntu archives if they wish. It could become the default on the desktop in 14.10 in October 2014, since that release won't have the burden of being a Long-Term Support edition.

Canonical has said Mir is the best option to power its Unity interface across desktops and mobile devices, but in doing so it broke with others in the Linux community supporting a rival technology, Wayland. Notably, an Intel developer said the company will refuse XMir patches contributed by Ubuntu.

"Some of the benefits that Mir will eventually offer include lower overhead in the display pipeline, more seamless transitions between display modes during the boot process, richer input handling that will make it easier to support things like touchscreen gestures, more seamless support for systems with switchable graphics hardware (like laptops that can dynamically shift between using embedded and discrete graphics), and better application interchange (which will help improve things like the clipboard and drag-and-drop)," Ryan Paul wrote in the Ars review of Ubuntu 13.10.

Before the 13.10 release, Bacon told Ars that Canonical will have an easier time maintaining Mir than Wayland in Ubuntu because Mir is lighter-weight.

"We want Wayland to do less, we want it to be thinner," he said. "Wayland has in many ways a wider scope; it tries to be more things to more people than we wanted a display server to be."

Canonical's Oliver Ries, head of engineering product strategy, said in March of this year that getting Wayland onto a mobile device would be too challenging. "[T]here is the rather sizable challenge of pulling Wayland/X onto a mobile device, working with SoCs on driver support, tuning this stack for power consumption and performance and dealing with other issues of a stack that hasn’t been designed for a convergence setup as we envision it," he wrote at the time.

Mir and Unity 8 are already powering Ubuntu for phones, which was released with 13.10. Unity 8 with Mir will power the first stable release of Ubuntu for tablets in 14.04.

Ubuntu, Android, and 64-bit ARM

Shuttleworth answered a few other questions, including whether Ubuntu for phones and tablets will be able to run Android applications. The answer is yes, but likely not in the first releases.

"That certainly is a goal," he said. "To us, Android is Java and Java runs really well on Ubuntu. Yes, that's a goal. It's not a primary focus for us in this cycle."

Canonical will try to make dual-booting of Android and Ubuntu as easy as possible. "Dual-boot with Android is something I've seen in the labs, as it were. We think that would be a very cool way to encourage people to keep track of Ubuntu development and Android evolution," he said.

Canonical will not be making its own tablet hardware, Shuttleworth said. He admitted to being "a little crushed inside" when the Ubuntu Edge smartphone wasn't funded, but he said multiple "household names" are looking to put Ubuntu on tablets and phones.

Canonical has been working on supporting ARM chips for several years and is now focusing on compatibility with 64-bit ARM processors.

"You've seen 64-bit mobile processors from Apple, we will see 64-bit mobile processors from other companies on which Ubuntu might run, and we're seeing 64-bit ARM-based processors for hyper-dense server infrastructure as well," Shuttleworth said. "ARM 64 is going to be a key focus for us this cycle."