如果要移除本地的镜像，可以使用 docker rmi 命令。注意 docker rm 命令是移除容器。
$ sudo docker rmi training/sinatra
Untagged: training/sinatra:latest
Deleted: 5bc342fa0b91cabf65246837015197eecfa24b2213ed6a51a8974ae250fedd8d
Deleted: ed0fffdcdae5eb2c3a55549857a8be7fc8bc4241fb19ad714364cbfd7a56b22f
Deleted: 5c58979d73ae448df5af1d8142436d81116187a7633082650549c52c3a2418f0
注意：在删除镜像之前要先用 docker rm 删掉依赖于这个镜像的所有容器。