If you develop Android appication on Linux and have ran into an issue with testing on a physical device the following script might help. All you have to do is plug in your phone and restart ADB. To use this script just cd into the directory containing ADB. It is usually /home/USERNAME/Android/Sdk/platform-tools.

#! /bin/bash
cd /home/jcasey/Android/Sdk/platform-tools
sudo ./adb kill-server
sudo ./adb start-server
sudo ./adb devices

Give this a try and hopfully it fixes your problem.