The wicked adb devices ?????? no permissions error

I have solved it.

I searched it a lot. Did not get a complete solution.

So what I did was:

1) Plugin your Android.
2) >lsusb
gives 
Bus 002 Device 006: ID 18d1:d002 Google Inc.
3) create a new file in /etc/udev/rules.d
by the name of 99-android.rules
Insert the following:
SUBSYSTEM=="usb", ATTRS{idVendor}=="18d1", MODE="0666"
4) Phone prompts for permission grant
5)adb kill-server
6)adb devices (this automatically starts the server as well)
List of devices attached
xxxxxxxxxxx    device
7)Enjoy!