有些系统直接 apt install docker.io就能装上，有些就不行，或者运行报错：

    • mkdir /app read-only filesystem
    • docker socket not found

    root 操作：

    1. apt-get update
    2. apt install apt-transport-https ca-certificates curl software-properties-common
    3. curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add -
    4. add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu bionic stable"
    5. apt update
    6. apt-cache policy docker-ce
    7. apt install docker-ce