What is this permission problem with adb?

I would like to transfer files between a phone (Harmony 2.0.0) and a Linux laptop with USB connection between them. I try to use adb by following https://www.reddit.com/r/linuxquestions/comments/hde7f4/enable_linux_mounting_of_android_usb_device_for/fvl8gyp/ , but why do I have the permission problem? $ adb devices * daemon not running; starting now at tcp:5037 * daemon started successfully List of devices attached A7Q0218123000244 no permissions; see [http://developer.android.com/tools/device.html] $ adb shell adb: insufficient permissions for device See [http://developer.android.com/tools/device.html] for more information I can't find anything useful in the link http://developer.android.com/tools/device.html