Android ADB debugging in Linux

adb devices shows: ????? no permissions  

This is taken from:

Find the correct vendor Id:

sudo vim /etc/udev/rules.d/51-android.rules

Add the following and put in the correct ID where the *'s are
SUBSYSTEM=="usb", ATTR{idVendor}=="****", MODE="0666", GROUP="plugdev"

sudo chmod a+r /etc/udev/rules.d/51-android.rules

Now plug in your device and run:
adb devices

If it still doesn't show up, try unplugging your phone.
Then run:
adb kill-server
adb start-server

Plug in your phone and run:
adb devices