Nexus device not listed (Android Development) - Linux Ubuntu

I got the following message when I run "adb devices"

List of devices attached
???????????? no permissions

To fix this problem I followed the below steps,

1. Logged in as root User

2. vim /etc/udev/rules.d/51-android.rules and added the following lines

SUBSYSTEM=="usb", SYSFS{idVendor}=="0bb4", MODE="0666"
SUBSYSTEM=="usb", SYSFS{idVendor}=="18d1", MODE="0666"

3. /etc/init.d/udev restart

You may also need to restart the adb daemon: [as a *ROOT* user]

./adb kill-server
./adb start-server
./adb devices


This should fix the problem :)