After upgrading to Android Jellybean (4.2.2) the 'adb (Android Debug Bridge)' program failed to connect my Android mobile phone. Running 'adb devices' in the terminal showed error: device offline message.
Recently Android switched to MTP (Media Transfer Protocol). Unfortunately MTP support has some issues. For now I have to resort to using 'adb' command to work with my Android mobile phone.
Digging around the Internet, I learned that Android Jellybean has a new security feature. You need to do RSA key fingerprint verification with the PC. Otherwise the Android device will be reported as offline.
How to Fix ADB Device Offline Error
Here are the steps to connect to your Android device with adb.
- Get the latest version of adb. Update using Android SDK android program: 'android update adb'
- Restart adb server with 'adb kill-server'
- Unplug and reconnect the device to a different USB port
- Repeat last two steps until you see 'Allow USB Debugging?' dialog on your android device.
- Select 'Always allow from this computer' option
Now you can talk to your Android device using the adb commands.