Fragmentation has arrived in the display server area of the Ubuntu community, as the parent Ubuntu distribution forges it's own path, and its KDE-focused derivative remains on the X display stack used by the vast majority of modern Linux distributions.
In an update delivered to the Ubuntu development mailing list, Canonical director of product strategy engineering Oliver Ries detailed how Ubuntu would transition over to the new Mir-driven display stack.
Ubuntu 13.10 will use XMir, a stack where X and Unity 7 run on top of the Mir system compositor by default, with a fallback option of running X without any Mir driver support. This edition will be supported for nine months.
By Ubuntu 14.04 LTS, a long-term release that will be supported for five years, the fallback X option will be removed. This release is intended to have full Mir driver support.
Come October 2014, when Ubuntu 14.10 is due, the entire Mir stack running Unity 8 as session shell will be the default option. Ubuntu 14.10 will be supported for nine months, and include rootless X support for legacy X applications.
"Using Mir as a X compatible system compositor in 14.04 which can host any Desktop Environment that is running on X today, will allow all dependent Ubuntu derivatives to run on top of this stack in 13.10 and 14.04 without any changes needed on their side," said Ries.
Ries pointed to a YouTube clip that showed Unity 7, GNOME, KDE, XFCE, and LXDE running on XMir.
"Canonical is committed to supporting XMir for five years during the 14.04 lifecycle, which will give derivatives enough time to evaluate the graphics stack landscape and to make informed decisions when they are ready," he said.
One derivative that is not waiting to make a decision is Kubuntu. The KDE-focused spin on Ubuntu has decided that it will be choosing to move to a display stack based on Wayland.
"Here at Kubuntu, we still want to work as part of the community development, taking the fine software from KDE and other upstreams and putting it on computers worldwide," wrote Kubuntu lead Jonathan Riddell.
"So when Ubuntu Desktop gets switched to Mir, we won't be following. We'll be staying with X on the images for our 13.10 release now in development, and the 14.04LTS release next year. After that, we hope to switch to Wayland, which is what KDE and every other Linux distro hopes to do."
Riddell said that another layer, such as Mir, between KDE's windows manager, KWin, and the monitor is only likely to produce more bugs that the KWin team would need to fix, and for that reason, Mir would not be part of any Kubuntu image.
"What's unknown is what happens when an Ubuntu Desktop user installs Kubuntu Desktop or vice versa. We'll have to find a way to deal with that in a sensible manner."
Although Wayland would be mostly synced from Debian, Riddell said that maintaining it would be "fiddly", as would maintaining the live CD system containing three display servers in form of X, Wayland, and Mir.
Moving to Mir is far from the first time that Ubuntu has pledged to forge a different route from all other Linux distributions. Rather than continuing to have a modified GNOME desktop as its default environment, the decision was made to move to the Unity desktop instead. Beginning with Ubuntu 11.04, the Unity desktop was made the new default environment, and many users were .
Following the move to Unity, Canonical founder Mark Shuttleworth announced in Novemeber 2010 that the Linux distribution would make the transition over to Wayland.
At the time, Shuttleworth said that it would be realistic to expect the first usable images of Unity on Wayland to appear within a year, but that it could take up to four or five years to move the ecosystem.
"Progress on Wayland itself is sufficient for me to be confident that no other initiative could outrun it, especially if we deliver things like Unity and uTouch with it," Shuttleworld said.
Come 2013, though, Ubuntu shifted its weight behind creating its own display stack based on its new Mir display sever.
Mir is expected to power not only the standard Ubuntu desktop, but also thesystem.