In this case, it was a digital camera problem. Since we bought our Canon PowerShot SD600 last December, I’ve used KDE’s digiKam to transfer and manage the photos. DigiKam detected the camera and accessed the photos right out of the box, no configuration needed beyond telling it to remember the model. But something changed in the last two weeks, and last night I started getting an error message: Failed to connect to the camera. Oddly enough, it could still detect the camera when it was connected. But it couldn’t display or download the images.

I searched all over, hitting dead end after dead end, until I got a hint that it was a permissions problem. That’s when I hit the command line to start troubleshooting.

Digikam uses a library called gphoto2 to access cameras. It has utilities that you can run from the command line for testing. I ran gphoto2 --auto-detect, which dutifully reported the correct camera. I ran gphoto2 -l to list the folders on the camera, and it spit out an error including the phrase: Could not claim the USB device. The interesting thing was, if I ran the same command as root, it was able to see the folders.

Way back when, Linux used a static list of devices in /dev. Now that everyone is constantly connecting and disconnecting devices with USB, Firewire, Bluetooth etc., that’s not practical. Most modern Linux distributions use one method or another to dynamically build that list from what’s actually connected to the computer, and react when new devices are plugged in. Fedora 7 uses udev to identify and configure devices. I had to figure out how to tell udev to give me write access.

I finally found the gphoto documentation on setting permissions, and found the command I needed: print-camera-list, which will build a list of rules for udev to use when someone attaches a camera. Unfortunately, the directions were slightly out of date. Instead of adding a “version 0.98″ option, it wanted “udev-rules-0.98″.

So the command I used (as root) was this:

/usr/lib/libgphoto2/print-camera-list udev-rules-0.98 group users mode 0660 > /etc/udev/rules.d/90-libgphoto2.rules

Note that where it says “users” you should substitute the name of the group your account belongs to. (In Fedora, that might actually be the same name as your username, since it likes to create a group just for you.)

It took me about an hour to track this down, since initial searches sent me looking in the wrong direction. I’m hoping this blog post will save someone else a little time and frustration.

Update (June 2008)

I’ve run into a different problem with Fedora 9. In this case, I’m running digiKam under the GNOME desktop. GNOME can mount the camera now, so it auto-mounts and pops up a filesystem window. But when I try to access the camera in digiKam, I get the same error message about not being able to connect.

It turns out this one’s just a conflict: either the virtual filesystem or digiKam can access the camera, but not both at once. I just right-clicked on the icon on the desktop, unmounted it, and was able to connect in digiKam.

It should be more flexible (and run faster) than CD-based distributions like Knoppix or Mandrake Move [archive.org], although it’s bulkier than carrying a CD and a keychain.

Hmm, I wonder if I could get Damn Small Linux to boot off a USB keychain…