1. Pull the image through the docker pull ubuntu:12.04 command, and find that the current directory has not changed.
2. Switch to the docker directory
[root@iZwz9fedjw2xvy6fvxfnxgZ zxy]# cd /var/lib/docker [root@iZwz9fedjw2xvy6fvxfnxgZ docker]# ll total 36 drwx------ 3 root root 4096 Mar 12 11:45 containers drwx------ 5 root root 4096 Mar 9 18:36 devicemapper drwx------ 3 root root 4096 Mar 9 17:44 image drwxr-x--- 3 root root 4096 Mar 9 17:44 network drwx------ 4 root root 4096 May 2 10:10 plugins drwx------ 2 root root 4096 Mar 9 17:44 swarm drwx------ 2 root root 4096 May 2 10:23 tmp drwx------ 2 root root 4096 Mar 9 17:44 trust drwx------ 3 root root 4096 Mar 12 11:45 volumes
3. Each folder in the containers directory represents an image
[root@iZwz9fedjw2xvy6fvxfnxgZ docker]# cd containers/ [root@iZwz9fedjw2xvy6fvxfnxgZ containers]# ll total 4 drwx------ 4 root root 4096 May 2 10:43 5625c8fcd1413522ebe6ed4bcec116763fefa3d4de4ef93c83079f6fb515b356
4. Related information in the devicemapper folder in the image directory
[root@iZwz9fedjw2xvy6fvxfnxgZ containers]# cd ../image/devicemapper/ [root@iZwz9fedjw2xvy6fvxfnxgZ devicemapper]# ll total 16 drwx------ 4 root root 4096 Mar 9 18:36 distribution drwx------ 4 root root 4096 Mar 9 17:44 imagedb drwx------ 5 root root 4096 Mar 9 18:36 layerdb -rw------- 1 root root 591 May 2 10:23 repositories.json
5. The mirroring information is recorded in the repositories.json file
[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