This question is an exact duplicate of:
When I run 'sudo apt-get update' the response I get is 'AppStream cache update failed.' Have read through all of the questions that may already have your answer and none of them are even in the ballpark of the question I am asking.Two hours ago wiped my hard drive clean and reinstalled ubuntu 16.04.1. The very next thing I did was run 'sudo apt-get update', which failed. Don't see how I can express this plainer or be more specific.