emulator is not listed in connected usb devices even though the usb debugging is on in android studio

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 sudo kill -9 (since my computer was freezing and I had no other choice), my usb connected device list is empty.

What I've tried:

• I checked the developer options and usb debugging mode was still enabled.
• I tried to restart AVD manager from inside android studio; still got nothing in the connected usb device list.
• I tried to restart the android studio; still the same.
• I tried to restart the abd from command line with sudo abd kill-server and sudo abd start-server; nothing changed.
• I even rebooted my computer; still nothing shown in the list.

Notes:

1. I run android studio with root permissions; so I assume it can perform required actions with root access.
2. I checked connected usb devices from command line with sudo adb devices -l and my emulator was not listed there either.

I tried the solution here by Deepak Kumar and it worked. It is:

1. Go to Phone Setting > Developer options > Revoke USB debugging.
2. Turn off USB debugging and Restart Again.