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

How to get connection to device working using adb command line:

USB debugging enabled on phone and phone connected.

I am exercising these commands on linux(redhat and ubuntu) but same commands work under the hood on windows. The device manager runs adb commands. You can find a console in your device manager or regular command-line works if you set up your paths to SDK.

If you can run adb and see something like ???????? in devices list ..

$ android-studio/sdk/platform-tools/adb devices
List of devices attached 
????????????    no permissions

You might be running the adb server as a regular user. You might have to run the adb server as root. So kill the server as regular user and start it as root.

$ adb kill-server
$ which adb
$ sudo <fullpath>/android-studio/sdk/platform-tools/adb start-server

Now look at adb devices list, if it is first time this machine connects to this phone you will see "unauthorized".

$ adb devices
List of devices attached 
MWS0216A31xxxxxx    unauthorized

At this point on phone you should have dialog popped up and you can tap ok to authorize. Then you should see "device" in the devices list and commands like shell/push/pull/sync/backup... should work.

$ adb devices
List of devices attached 
MWS0216A31xxxxxx    device

$ adb shell "uname -a; df; ls /storage/sdcard0/Download"
Linux localhost 3.10.90-g2ff1b22 #1 SMP PREEMPT Tue Dec 27 17:12:50 CST 2016 aarch64
Filesystem               Size     Used     Free   Blksize
/dev                     1.3G   108.0K     1.3G   4096
/sys/fs/cgroup           1.3G    12.0K     1.3G   4096
/mnt                     1.3G     0.0K     1.3G   4096
/sys/fs/cgroup/pids: Permission denied
/system                  2.4G     2.3G   106.8M   4096
/cust                  492.0M   327.7M   164.3M   4096
/cache                 248.0M   160.0K   247.8M   4096
/splash2: Permission denied
/3rdmodem               59.0M     4.9M    54.1M   1024
/3rdmodemnvm: Permission denied
. .
/storage                 1.3G     0.0K     1.3G   4096
/data                   25.1G    10.9G    14.2G   4096
/mnt/runtime/default/emulated: Permission denied
/storage/emulated       25.1G    11.2G    13.8G   4096
/mnt/runtime/read/emulated: Permission denied
/mnt/runtime/write/emulated: Permission denied
.
.

Lovely jubly. Hopefully.