Mount Nexus One SD card on PC with Ubuntu Linux

If you are trying to connect the Nexus One to Ubuntu via USB and it keeps disconnecting and you get the following messages when you run dmesg in a terminal:

[14082.844359] sd 23:0:0:0: [sdb] Sense Key : Not Ready [current]
[14082.844371] sd 23:0:0:0: [sdb] Add. Sense: Medium not present
[14082.844386] end_request: I/O error, dev sdb, sector 24
[14082.854502] sd 23:0:0:0: [sdb] Device not ready
[14082.854512] sd 23:0:0:0: [sdb] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE

The fix is turn on USB debugging for the Nexus One:

On the Nexus One, go to Settings -> Applications -> Development and check USB debugging and say OK to the warning. Connect the Nexus One via USB to the Ubuntu machine and it should connect fine.

Solution source: http://code.google.com/p/android/issues/detail?id=5880