Troubleshooting: "No Permissions" Warning in ADB Devices

When running adb devices, output similar to the following may occur:

List of devices attached
025ab6b8e2869678    device
00dc300977a1bf59    no permissions (udev requires plugdev group membership);
see [http://developer.android.com/tools/device.html]

Solution Check to see if USB mode is charging. If it is, change the mode to File Transfer.