I finally found the source of the unbearable kernel panic I get every time I log in (via GDM) with Dapper pre-release. It’s been happening for about a month now. The cause:

A desktop wallpaper

That’s right. While we can build systems to recognize faces from low-dimensional subspaces based on the principal components of images; while we can construct scalable networks with no centralization that service billions of users; while we can cram a full PC into an LCD monitor, setting a desktop wallpaper still eludes us.

Sorry. Manually rebooting frequently after kernel panics can try one’s patience. The cause is either nautilus (which displays the desktop wallpaper) or the ATI drivers.

When using the “radeon” driver (OSS, non-accelerated), X is happy to simply crash out with no warning or log, but thankfully it leaves my kernel in a state of sanity.

When using the accelerated ATI drivers (”fglrx”), however, the crash occurs in the same place, but this time it takes the entire system with it. The kernel panic goes something like this:

kernel panic - not syncing: Fatal exception in interrupt

… and the rest of the error message? Well, the rest of the message is cut off at the bottom of my screen, because Ubuntu thinks my terminal is two lines bigger than my monitor, such that the top and bottom lines of terminal output are cut off and not displayed (working on the terminal framebuffer is a pleasure).

To work around this problem, I can ssh in from another computer, move the wallpaper file so that nautilus can’t find it when it starts up, and the next login goes smoothly (the wallpaper defaults to a solid brown color). It’s not the bitmap I’m using, either; it occurs with any bitmap.

Google has a modicum of information about this problem, so maybe this will help someone.