在虚拟机上通过docker build 打包镜像时报错

Error parsing reference:"ubuntu:20.04 AS build" is not a valid repository/tag:
invalid reference format

原因是docker版本太低导致

1.卸载docker

yum remove docker*

2.在线安装docker,如果源上有的话

yum install docker-ce

docker-ce试过20版本依赖太多，装不上，这里用18版本的

https://download.docker.com/linux/centos/7/x86_64/stable/Packages/docker-ce-18.09.8-3.el7.x86_64.rpm

docker-ce-cli

https://download.docker.com/linux/centos/7/x86_64/stable/Packages/docker-ce-cli-18.09.8-3.el7.x86_64.rpm

containerd.io

https://download.docker.com/linux/centos/7/x86_64/stable/Packages/containerd.io-1.4.12-3.1.el7.x86_64.rpm

确认yum源配置了镜像文件（避免其他依赖没装上）,即通过 yum install 安装以上rpm包