清理docker内不用的镜像、缓存

docker在运行时，随着时间的推移，会产生很多垃圾文件，占用大量的空间，其实一条命令就可以清理了。

清理docker内不用的镜像、缓存

docker system prune -a

则会清理一下不用的镜像等等，节省空间。

root@debian:~# docker system prune -a
WARNING! This will remove:
  - all stopped containers
  - all networks not used by at least one container
  - all images without at least one container associated to them
  - all build cache

Are you sure you want to continue? [y/N] y
Deleted Containers:
b9dad209e8093d3827e6a048a45b6eb5ee4102c951e923adef34cdb08b5dc689

Deleted Images: