1、通过docker pull ubuntu:12.04 命令拉取镜像，ll发现当前目录并没有什么变化。
2、切换到docker目录
[root@iZwz9fedjw2xvy6fvxfnxgZ zxy]# cd /var/lib/docker
[root@iZwz9fedjw2xvy6fvxfnxgZ docker]# ll
total
drwx------ root root Mar : containers
drwx------ root root Mar : devicemapper
drwx------ root root Mar : image
drwxr-x--- root root Mar : network
drwx------ root root May : plugins
drwx------ root root Mar : swarm
drwx------ root root May : tmp
drwx------ root root Mar : trust
drwx------ root root Mar : volumes
3、containers目录下的每一个文件夹代表一个镜像
[root@iZwz9fedjw2xvy6fvxfnxgZ docker]# cd containers/
[root@iZwz9fedjw2xvy6fvxfnxgZ containers]# ll
total
drwx------ root root May : 5625c8fcd1413522ebe6ed4bcec116763fefa3d4de4ef93c83079f6fb515b356
4、image目录下的devicemapper文件夹下相关信息
[root@iZwz9fedjw2xvy6fvxfnxgZ containers]# cd ../image/devicemapper/
[root@iZwz9fedjw2xvy6fvxfnxgZ devicemapper]# ll
total
drwx------ root root Mar : distribution
drwx------ root root Mar : imagedb
drwx------ root root Mar : layerdb
-rw------- root root May : repositories.json
5、其中repositories.json文件里记录了镜像的信息
[root@iZwz9fedjw2xvy6fvxfnxgZ devicemapper]# cat repositories.json
{"Repositories":{"docker.io/centos":{"docker.io/centos:7.2.1511":"sha256:0a2bad7da9b55f3121f0829de061f002ef059717fc2ed23c135443081200000e","docker.io/centos@sha256:7c47810fd05ba380bd607a1ece3b4ad7e67f5906b1b981291987918cb22f6d4d":"sha256:0a2bad7da9b55f3121f0829de061f002ef059717fc2ed23c135443081200000e"},"docker.io/ubuntu":{"docker.io/ubuntu:12.04":"sha256:5b117edd0b767986092e9f721ba2364951b0a271f53f1f41aff9dd1861c2d4fe","docker.io/ubuntu@sha256:18305429afa14ea462f810146ba44d4363ae76e4c8dfc38288cf73aa07485005":"sha256:5b117edd0b767986092e9f721ba2364951b0a271f53f1f41aff9dd1861c2d4fe"}}}[root@iZwz9fedjw2xvy6fvxfnxgZ