Hack 93. Perfect USB Devices with Project Utopia

Kick your desktop into the Plug and Play world with your USB devices.

Few would argue that USB has not had a tremendous impact on the computer world. Everything from sound cards to network cards to lamps and beyond is available with a USB connector hanging off the side.

Linux support for devices has traditionally been a slightly crufty area. Devices that are plugged in usually require several manual steps before the OS recognizes them, and they are accessible to the user. But in the last two years the ease of hardware handling has improved dramatically. One of the major projects to work on this problem is Project Utopia. This collection of developers has worked to create a software stack that enables you to plug a device into your USB port and have it just work. This stack includes the following tools:

udev: This tool replaces the kernel-managed /dev with an equivalent userspace that makes it easier for devices to be handled.
dbus: This allows programs to communicate with each other and respond to specific events.
Hardware Abstraction Layer (HAL): This component ties together the other technologies to provide information about system events, as well as an abstracted layer in which to interact with hardware. Traditionally, most programs that deal with hardware have done it in their own way, but HAL provides a consistent way of dealing with hardware while getting the benefits of device detection and other features.

In addition to these tools, you need to be running a 2.6 series kernel [Hack #89] and a recent version of linux-hotplug. Project Utopia is a fairly complex system to build, so I recommend you install the binary packages that are available for your distribution. If you are intent on compiling the source code, however, you should look at the documentation available at http://hal.freedesktop.org.

11.3.1. Install the Packages

You need to install the packages in the right order. If you are using a system that figures out the dependencies and installs them in the correct order (such as APT or portage), this should be easy for you. If you are installing the packages individually, here is the required order:

Kernel 2.6
linux-hotplug
udev
dbus
HAL

In addition, if you are using the GNOME desktop, you should install the GNOME Volume Manager. This package (often named gnome-volume-manager) requires the following packages to be installed:

python-gnome2
libgnomeui
gnome-common
libglade2

You probably have some of these packages available already.

11.3.2. Configure the Automounter

When you plug a device into the system, you want to be able to automatically access the device. For units such as digital cameras and other USB mass storage devices, you ideally want to plug in the device and be able to use it right awayno more manual mounting of disks. On a Linux system, mounted disks are typically managed by /etc/fstab. One option for automatically mounting inserted media uses this file. This program, called fstab-sync, is part of the HAL package and it modifies /etc/fstab each time a device is plugged in and used. When you install the HAL package, fstab-sync is installed automatically for you.

Another option is to use pmount, written by Martin Pitt. This handy little tool replaces the mount command with a version that can be used in userspace so that nonroot programs can access devices. The Ubuntu distribution uses this method with a good degree of success, but it requires a little more work to get going. To use pmount you need to use a special patched GNOME Volume Manager. At the time of this writing the GNOME Volume Manager does not include built-in support for pmount, but you should check to see if a newer version with pmount support has been released by having a look on Google.

If the versions of GNOME Volume Manager available to you don't contain pmount, you will need to patch the GNOME Volume Manager source yourself and compile it. Before you do this, be certain you have the following programs installed:

pmount
python-gnome2-dev
libgnomeui-dev
libglade2-dev

You can download the source code to the GNOME Volume Manager from http://ftp.gnome.org/pub/GNOME/sources/gnome-volume-manager, and you can get the pmount patch from http://people.debian.org/~mpitt/gnome-volume-manager.pmount.patch. Extract the Gnome Volume Manager code to a work directory, copy the patch to that directory, and cd to the work directory. Then patch the code using this command:

foo@bar:~$ patch -p1 < ubuntu-pmount.diff

You might see some patch errors referring to a Debian control file. You can safely ignore these errors when you're not running on a Debian system. Finally, you can compile the code with this:

foo@bar:~$ ./autogen.sh
foo@bar:~$ make
foo@bar:~$ make install (you may need to be root to do this)

Now you have a patched GNOME Volume Manager that can use pmount.

11.3.3. Configure Your System

With the GNOME Volume Manager installed you can configure your system to respond intelligently when devices are plugged in. You configure this with the gnome-volume-properties tool. You should run this tool from the command line, and then check the "Mount removable drives when hot-plugged," "Mount removable media when inserted," and "Browse removable media when inserted" checkboxes. For the other options in the properties box, try the following commands:

Audio CDs: gnome-cd --unique --play --device %d
Blank CDs: nautilus --no-desktop burn:
DVD videos: totem dvd://
Digital cameras: /usr/share/gnome-volume-manager/gnome-volume-manager-gthumb.sh %h

These options enable the most common actions you will want when you insert new media into your computer.