GPhoto2
libgphoto2 is a portable library which gives access to hundreds of digital cameras. It can be used in any software that wants to control digital cameras settings or simply take some pictures with them. A list of projects using it is available here.
There is a command line interface to libgphoto2, named gphoto2. It can be used to verify what settings are available through the USB link of your camera but also to take pictures or make a simple intervalometer in shell programming. Pictures can be taken in the internal memory of the camera or transferred right away on the computer.
To use gphoto2 and software based on the libgphoto2 library, you will need to fix the rights of the USB device created for the camera. A simple way to do it is to change the group of the device to a group in which you are, for example:
# chgrp optical /dev/bus/usb/* # chgrp optical /dev/bus/usb/*/*
Using Gphoto2 CLI
A special page has been created for documentation of the list of properties that can be modified by gphoto2 and the values allowed for some of them.
The utility also allows picture to be taken and stored onboard the camera or downloaded to the computer. The computer can then replace the intervallometer and can be operated remotely without ever touching it, avoiding to lose the focus when mounted on a telescope.
Using a digital camera as webcam for planetary imaging
The project EOS Camera Movie Record (AUR package), using Gphoto2, allows the live view of a Canon EOS to be captured and used as a webcam. This proves to be a nice alternative to webcam imaging. See some results for this capture method here.
Tested with an EOS 1000D, it works fine. I just don't know how to specify what part of the image is used for the 5x magnified capture. If the program says "no auto camera found", it probably means that you don't have the rights to access the USB device, see above.