Keystore file doesn't exist

Linux & Mac command

keytool -list -v -keystore ~/.android/debug.keystore -alias androiddebugkey -storepass android -keypass android

Will give you SHA1, SHA256, MD5 for default debug key. And it can be used for developing and debugging with google play services.

For publication certificate just follow https://developer.android.com/studio/publish/app-signing.html

You said you are running the command from...

/Library/Java/JavaVirtualMachines/jdk1.8.0_20.jdk/Contents/Home/bin

Is your keystore file in that directory as well? If not then you need to specify the path to the keystore file, e.g.

keytool -list -v -keystore ~/somefolder/mystore.keystore

The keystore used should be the one used to sign the app. For Xamarin debug builds this will be the debug keystore located at /Users/[USERNAME]/.local/share/Xamarin/Mono\ for\ Android/debug.keystore. The command on OSX for this would be...

keytool -list -v -keystore /Users/[USERNAME]/.local/share/Xamarin/Mono\ for\ Android/debug.keystore -alias androiddebugkey -storepass android -keypass android

Or on Windows 7

keytool -list -v -keystore C:\Users\[USERNAME]\AppData\Local\Xamarin\Mono for Android\debug.keystore -alias androiddebugkey -storepass android -keypass android

I faced the same issue, but resolved via following command:

keytool -exportcert -keystore C:\Users\<USERNAME>\.android\debug.keystore -list -v

OS: Windows 7