Under the impression of loosing some really important data because of a damaged partition table on a USB flash drive I am developing a backup strategy for my system.
I know myself and so I decided that I need to automate this. While trying to figure out how one can run a script as soon as a specific drive is mounted, I came across DeviceKit. It’s the planned replacement of HAL and is used in Ubuntu Karmic. Udev is not an option for me, because I don’t want to mess around with mounting myself (and I hate running stuff as root…).
So here is what I found out about using DBus and DeviceKit in Python:
import dbus bus = dbus.SystemBus() proxy = bus.get_object("org.freedesktop.DeviceKit.Disks", "/org/freedesktop/DeviceKit/Disks") iface = dbus.Interface(proxy, "org.freedesktop.DeviceKit.Disks") #enumerates all devices print iface.EnumerateDevices() #gets the device kit path of a specific device path = iface.FindDeviceByDeviceFile("/dev/sdc1") #= "/org/freedesktop/DeviceKit/Disks/devices/sdc" #gets an object representing the device specified by the path device = bus.get_object("org.freedesktop.DeviceKit.Disks", path) #prints some XML that shows you the available methods, signals and properties print device.Introspect() #gets a proxy for getting properties device_prop = dbus.Interface(device, "org.freedesktop.DBus.Properties") #you need to specify an interface (properties could be ambiguous) print device_prop.Get("org.freedesktop.DeviceKit.Disks.Device", "device-mount-paths") #gets a proxy you can call methods on device_iface = dbus.Interface(device, "org.freedesktop.DeviceKit.Disks.Device") #unmounts the partition device_iface.FilesystemUnmount(dbus.Array([], 's'))
The DBus API of DeviceKit is documented here.
Now we want to be notified when a drive is mounted:
import dbus import gobject from dbus.mainloop.glib import DBusGMainLoop def device_added_callback(device): print 'Device %s was added' % (device) def device_changed_callback(device): print 'Device %s was changed' % (device) #must be done before connecting to DBus DBusGMainLoop(set_as_default=True) bus = dbus.SystemBus() proxy = bus.get_object("org.freedesktop.DeviceKit.Disks", "/org/freedesktop/DeviceKit/Disks") iface = dbus.Interface(proxy, "org.freedesktop.DeviceKit.Disks") #addes two signal listeners iface.connect_to_signal('DeviceAdded', device_added_callback) iface.connect_to_signal('DeviceChanged', device_changed_callback) #start the main loop mainloop = gobject.MainLoop() mainloop.run()
A typical output when a flash drive is plugged in looks like this:
Device /org/freedesktop/DeviceKit/Disks/devices/sdc was added Device /org/freedesktop/DeviceKit/Disks/devices/sdc1 was added Device /org/freedesktop/DeviceKit/Disks/devices/sdc1 was changed
With this knowledge I’m currently working on a little python script that runs in background and executes a shell script when a file system is mounted. I’ll post it, when it’s finished 
This has to be the easiest article of starting to use the DeviceKit API I’ve seen so far. I’ve been using HAL + DBus for some time but have to migrate due to it being completely dropped in the upcoming Ubuntu Lucid release. Thanks for taking the time to post this article up!