How to disable the guest feature WITHOUT having to be the only user
This one works for me on Android 5.0.1 and 5.1.1

Open a terminal, grant it root access then run

settings put global guest_user_enabled 0


You don't need to add fw.max_users=1 to your build.prop. It prevents more accounts from being created besides disabling guest feature. The above method only shuts off guest while leaving the "more users" option available.



Alternatively, if you don't need dynamically creating &amp; deleting extra users, you can create a few before proceeding.

Add this line to your build.prop.

fw.max_users=2


The multi-user settings will stil be available from your Settings app, but a guest (or any extra account) is kept from being created.