If you have tried to connect any new device to already setup ubuntu where adb was working fine for another device OR you got a new Ubuntu desktop/laptop and wants to setup adb, there are higher chances you may see the error as below, as you attempt to do “adb devices” or “adb shell” to access adb console.
$ adb devices List of devices attached ???????????? no permissions
There are various reasons you may see this error even though everything was working in another device/host setup, some of the possible solutions are listed as below,
1. Disconnect and Reconnect your device using USB
This is very simple first thing you can try to see if the auto setup after re-connection resolves this error.
2. Kill and restart adb server while USB is already connected.
$ adb disconnect
$ adb kill-server
$ adb start-server
3. Try with sudo permission if you have sudo access
$ sudo adb kill-server
$ sudo adb devices
4. Possibility of some issue with udev, try fix as per our another post, “Solved: no permissions (user in plugdev group; are your udev rules wrong?)”