It seems that the Android debugger (adb) has problems on Ubuntu when trying to connect to a physical device, a Nexus One is this case. The issue is relating to user permissions with the debugger being unable to access the usb device. I have seen a number of solutions for this with the most common being simply killing the adb process and restarting it as root.
cd android-sdk-linux_x86/platform-tools adb kill-server sudo adb start-server adb devices
But unfortunately this was not sufficient to resolve the problem for my configuration and also it would be necessary to restart adb on every system restart. A more permanent solution appears to be adding a rule to udev to permit usage of the device.
sudo gedit /etc/udev/rules.d/51-android.rules
and paste the following lines
SUBSYSTEM=="usb", SYSFS{idVendor}=="0bb4", MODE:="0666"
SUBSYSTEM=="usb", SYSFS{idVendor}=="18d1", MODE:="0666"
The 0bb4 in the idVendor property identifies the device (Nexus One), you can list the currently connected usb devices on your machine running the command lsusb, from here you will be able to identify the vendor id for your android device.
sudo restart udev cd android-sdk-linux_x86/platform-tools ./adb kill-server ./adb start-server ./adb devices
Even with this second solution be sure to physically disconnect and reconnect the handset.
