Mir
 All Classes Namespaces Files Functions Variables Typedefs Enumerations Enumerator Friends Macros Groups Pages
Debug for XMir

What is XMir ?

In order to help with debugging, it's important to understand what XMir is and what bugs are likely to occur. XMir is not a replacement to X and does not alter X or compiz window management functionality in the current Ubuntu stack. XMir is an addition to the system. XMir enables Mir to be employed as a system compositor under the X stack, in this configuration Mir composites the greeter and the desktop sessions.

XMir is currently targeted at the Ubuntu 13.10 release as being the default configuration. It currently supports open source graphics drivers based on Mesa, Nouveau and Radeon. Once XMir is installed and properly configured, upon boot or restart of the LightDM daemon, Mir will determine if there is proper driver support; in the instance where proprietary drivers not supporting the Mir driver model are detected, LightDM will continue to boot into the standalone X configuration without error. From a visual perspective on Ubuntu desktop, XMir and standalone X are identical (note, currently there is an X cursor present on XMir but this soon be disabled, making the experience truly identical and indiscernible without checking on what processes are running, see Using Mir on a PC).

How to toggle between XMir and standalone X ?

In order to return to a standalone X configuration, comment out the following line in /etc/lightdm/lightdm.conf.d/10-unity-system-compositor.conf to look to look like this:

[SeatDefaults]
#type=unity

Simply reboot or restart LightDM. To reverse the process, simply comment the line back in to enable XMir.

Most common bugs

At the moment, the most common bugs are related to failures to boot into XMir. Due to the robust fallback mechanisms in place, most failures will result in completing the boot sequence standalone X configuration, when you expected XMir.

  1. First check your /etc/lightdm/lightdm.conf.d/10-unity-system-compositor.conf has type=unity properly enabled.
  2. When logging a bug, please include the log files contained in the /var/log/lightdm/ directory. Note, it is good to inspect the last update to these files to see if they were written to in your boot attempt, obviously if they were not updated their contents are irrelevant. The most important of these files is likely the lightdm.log and unity-system-compositor.log. You are more than welcome to inspect these files, frequently there will be an error statement in unity-system-compositor.log which can be traced back into the source code for further debug.
  3. If you have the experience of booting to a black screen which seems frozen, you may attempt to switch VT's by selecting <Ctrl+Alt+F8> to see if there is a UI present. Alternatively, <Ctrl+Alt+F1>, login at the console, copy out the log files mentioned above, then toggle back to standalone X as described above and rebooting.

Other bugs

If you experience a UI lock up or a crash, it would be helpful to double check for X backtracing which can be found here: https://wiki.ubuntu.com/X/Debugging

Note, it is highly unlikely you will see any visual corruption due to XMir. If you experience a visual corruption during use, it is most likely that it a bug that exists in the standalone X Ubuntu configuration. Please attempt to toggle back to the standalone X configuration and replicate the use case. If you succeed in only being able to repeat the visual corruption in XMir and not in standalone X, please file a bug with a detailed description of hardware used, XMir component versions used and the use case steps. You may check the versions of key XMir components by the following

dpkg -s libmirclient3 | grep Version
dpkg -s libmirserver0 | grep Version
dpkg -s lightdm | grep Version
dpkg -s unity-system-compositor | grep Version

Copyright © 2012,2013 Canonical Ltd.
Generated on Fri Apr 11 21:14:53 UTC 2014