Lightdm Bugs: What You (the Bug Filer) Should Know

I’ve been spending some time off and on cleaning and working on up the bugs in the lightdm project. Unfortunately someone who takes on this task, lightdm ends up with a lot of bugs that are not necessarily lightdm bugs and also lots of bugs with incomplete information. In a perfect world, everyone who was going to file a lightdm bug would read this, for now I’ll settle for spreading this information to anyone who reads my blog.

First a bit about the architecture. The job of the display manager (prior to lightdm) was to be a daemon, manage logins and sessions, run the display server, and provide a GUI to interact withe the user. Unfortunately since everyone has a favorite GUI technology, we ended up with a ton of different Display Managers (GDM, XDM, KDM, etc). The idea with lightdm was to separate the back-end work from the GUI. Everyone could re-use the back-end (lighdtm) and write their own GUI, also called a greeter, on top. So that’s where we are now, lightdm is a daemon process that manages everything, and a greeter, usually unity-greeter for Ubuntu or lightdm-gtk-greeter for Xubuntu deals with the user interaction. A PDF presentation on the architecture from the Desktop Summit is available here. Note: I assume Kubuntu uses the lightdm-qt-greeter but I’m not sure, if you know please comment here.

So why should you care about the architecture just to file a bug? The reason is that if you get your bug to the right package it will speed up the response. So here’s a real basic decision tree for you to follow when deciding what package to file against:

  1. Is the issue with something you’re seeing on the screen?  If so, it’s probably a greeter bug. If you’re using default Ubuntu, file against unity-greeter. If you’re using Xubuntu file against lightdm-gtk-greeter. Special case: Did the greeter load but the graphics look a little screwed up?  That could be an Xorg driver issue.
  2. If no greeter started, if you started in “low graphics mode”, or it doesn’t fit with case number 1 above, file it against lightdm and we can move it later if we need to.
For all bugs you will also get a much better response if you provide full and correct information from the beginning. This means providing the following details:
  • Like all Ubuntu bugs, you need to include steps to reproduce.
  • For all bugs we need the version of ligthdm you are using and the name of and the version of the greeter you are using. If you don’t know which greeter you are using, you can look at /etc/lightdm/lightdm.conf and check out the line that contains greeter-session.
  • If you have a greeter problem, for example, some of the graphical elements don’t look correct or you have problems entering your username, please include a screen-cap.
  • If you’ve messed with the standard lightdm config file, please attach /etc/lightdm/lightdm.conf to the bug.
  • For all greeter and lightdm bugs it helps us to include the contents of /var/log/lightdm.  You can tar them all up and post them. The logs will include your username, if you don’t want this to be known, then edit the logs and replace it with something else. The logs require root to read, so here’s a gather snippet you can copy:
sudo tar -cvzf ~/lightdm_logs.tgz /var/log/lightdm/*

If you plan on filing a bug against lightdm or a greeter following these steps can really help us out and hopefully get you a resolution quicker.  Thanks!

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