set up device for development (???????????? no permissions)

I am using a Samsung galaxy nexus phone (**Android 4.0** platform) . I am developing Android app on Ubuntu linux OS. I would like to run my application directly on the Samsung handset device, so I performed the following setup steps: 1. in my project `AndroidManifest.xml` file, added `android:debuggable="true"` to the `<application>` element 2. On the device, in the **Settings > Security** enabled **Unknown sources** 3. On the device, in the **Settings > Developer options** enabled **USB debugging** 4. On my computer, created the `/etc/udev/rules.d/51-android.rules` file with the following content: SUBSYSTEM=="usb", ATTR{idVendor}=="04E8", MODE="0666", GROUP="plugdev" 5. On my computer, run the `chmod a+r /etc/udev/rules.d/51-android.rules` command Then, on my computer I opened a terminal and executed the `adb devices` command, I got: List of devices attached ???????????? no permissions Since I did not see my device but only `???????????? no permissions`, I then run the following commands: adb kill-server adb start-server adb devices But I still got: List of devices attached ???????????? no permissions Why? What am I missing?