Ubuntu更换了source.list文件后，执行apt-get update，报如下错误
# apt-get update Hit:1 http://cn.archive.ubuntu.com/ubuntu xenial InRelease Hit:2 http://security.ubuntu.com/ubuntu xenial-security InRelease Hit:3 http://cn.archive.ubuntu.com/ubuntu xenial-updates InRelease Hit:4 http://cn.archive.ubuntu.com/ubuntu xenial-backports InRelease Reading package lists... Done E: The method driver /usr/lib/apt/methods/https could not be found. N: Is the package apt-transport-https installed? E: Failed to fetch https://download.docker.com/linux/ubuntu/dists/xenial/InRelease E: Some index files failed to download. They have been ignored, or old ones used instead.解决方法：apt-get install -y apt-transport-https
建议在替换source.list 之前就执行apt-get install -y apt-transport-https
