Você pode consultar o UDisks2 usando a API dbus do python:
Instale o python-dbus:
sudo apt-get install python-dbus
Execute este pequeno snippet de python:
cat <<EOF | python -
import dbus
bus = dbus.SystemBus()
ud_manager_obj = bus.get_object('org.freedesktop.UDisks2', '/org/freedesktop/UDisks2')
om = dbus.Interface(ud_manager_obj, 'org.freedesktop.DBus.ObjectManager')
for k,v in om.GetManagedObjects().iteritems():
drive_info = v.get('org.freedesktop.UDisks2.Drive', {})
if drive_info.get('ConnectionBus') == 'usb' and drive_info.get('Removable'):
print("Device Label: %s" % drive_info['Id'])
EOF
Com uma unidade USB conectada, recebo:
Device Label: Generic-Flash-Disk-EEA1EE5B