title: emulator is not listed in connected usb devices even though the usb debugging is on in android studio
body: <p>I have enabled developer options and usb debugging mode in my emulator in android studio and it was working very well; it was listed in my connected usb devices and I could select it for running my application. But once I killed the process from command-line with <code>sudo kill -9</code> (since my computer was freezing and I had no other choice), my usb connected device list is empty. </p>
  
  <p><strong>What I've tried:</strong></p>
  
  <ul>
  <li>I checked the developer options and usb debugging mode was still enabled.</li>
  <li>I tried to restart AVD manager from inside android studio; still got nothing in the connected usb device list.</li>
  <li>I tried to restart the android studio; still the same.</li>
  <li>I tried to restart the abd from command line with <code>sudo abd kill-server</code> and <code>sudo abd start-server</code>; nothing changed.</li>
  <li>I even rebooted my computer; still nothing shown in the list.</li>
  </ul>
  
  <p><strong>Notes:</strong></p>
  
  <ol>
  <li>I run android studio with root permissions; so I assume it can perform required actions with root access.</li>
  <li>I checked connected usb devices from command line with <code>sudo adb devices -l</code> and my emulator was not listed there either.</li>
  </ol>