Android device is not connected to USB for debugging (Android studio)

Question

I am trying to debug my application using a real device instead on the emulator. When I try to connect, it gives me the message:

USB device not found<

Answer 1

I had this problem occurring suddenly in Dell Ubuntu linux machine with Android Developer Studio. I did the following steps

    1. I opened "System Settings"
    2. Select the listed item "Software and Updates"
    3. Click on the tab "Additional Drivers"
    4. There was a mention about "Dell Inc: Unknown" and the option "Do not use use the device" selected. I selected the alternate driver mentioned and did an "Apply the Changes".

It started working.