It has been almost exactly one year since Canonical announced Mir, a replacement for the X window system. Mir was originally planned to become the default system in the Ubuntu desktop for the 13.10 (October 2013) or 14.04 (April 2014) releases, but it was delayed due to compatibility problems in multi-monitor setups. Those problems were with XMir, an X11 compatibility layer that ensures that Mir can work with existing applications built for X.

It made sense to not turn Mir on by default in the upcoming Ubuntu 14.04 because that's a Long Term Support release that must be stable for five years. But instead of saying that he intends to flip the switch later this year or in 2015, Canonical founder Mark Shuttleworth this week said he expects to do that by the 16.04 release in April 2016. Shuttleworth's comments don't necessarily rule out turning Mir on by default before 16.04, but it's not something Shuttleworth is ready to promise.

Speaking at one of Ubuntu's virtual developer summits, Shuttleworth noted that Mir is already the default on Ubuntu phones and tablets.

"We don't want to let a love of technology interfere with our mission to be great for the user," Shuttleworth said. Holding up an Ubuntu phone, he said, "this is a great place for us to set the bar very high in terms of performance, where we have freedom to get it right rather than worrying too much about compatibility."

On the desktop, users can install Mir themselves, but it won't be turned on by default for everyone just yet. "My expectation is that within the next 12 months you will see lots of people running Mir as their default display server, and by 16.04 it will be the default display server," Shuttleworth said. "There's lots of reasons why that will let us support more hardware, let us get much better performance, and let us do great things with some of the software companies we care about, who want to squeeze every bit of performance out of the hardware you've got."

Canonical built Mir to power the Unity user interface, a crucial part of building a consistent experience on phones, tablets, and desktops. In starting the Mir project, the company angered parts of the Linux community that are pushing Wayland, a display server that's headed for Fedora and other distributions. Notably, an Intel developer expressed his company's displeasure by refusing to accept Xmir patches into the company's open source graphics driver.

Canonical held firm, saying at the time that "Intel customers who use Ubuntu will not see any regressions as we will simply continue to support XMir in the Intel driver as part of Ubuntu. We believe in a healthy ecosystem of display servers, including X, Wayland, and Mir, and plan to continue to work with upstreams such as Intel to provide the best experience to end users and OEMs."

Ubuntu 14.04 for desktops is shipping with version 7 of Unity, whereas Unity 8 has been rolled out to mobile devices. Phoronix's Michael Larabel tested out Ubuntu 14.04 with various configurations, including one running Mir and Unity 8. He wasn't impressed.

"Everything went well with that testing before deciding to get into the unity8-desktop-session-mir and unity8-desktop-session-x11 testing," Larabel wrote. "When installing those packages on Ubuntu 14.04 and logging into the environment, it was a complete mess... Swipes didn't seem to work, the UI was barely responsive... and it was just an unusable mess at least when trying it out from a laptop. Granted, watermarked across the screen is "EARLY ALPHA NOT READY FOR USE."

Larabel is holding out hope that Mir "will end up being enabled by default in 2015 to allow for widespread testing and vetting ahead of the 16.04 Long-Term Support release." However, not turning Mir on by default provides "more time for upstream driver support too, which for now is non-existent," he wrote. "The binary AMD and NVIDIA Linux graphics drivers don't yet support Mir but not even the upstream open-source drivers have the support."