fix failed to fetch in apt-get update
This error can happen when fetching the latest repositories during "apt-get update" was interrupted, and a subsequent "apt-get update" is not able to resume the interrupted fetch. In this case, remove the content in /var/lib/apt/lists before retrying "apt-get update".
$ sudo rm -rf /var/lib/apt/lists/*
$ sudo apt-get update
If the above does not solve the problem, use the following commands instead.
$ sudo rm -R /var/lib/apt/lists/partial/*
$ sudo apt-get update