Docker lists the mirrors

Use docker images that are already local.

$ sudo docker images
REPOSITORY       TAG      IMAGE ID      CREATED      VIRTUAL SIZE
ubuntu           12.04    74fe38d11401  4 weeks ago  209.6 MB
ubuntu           precise  74fe38d11401  4 weeks ago  209.6 MB
ubuntu           14.04    99ec81b80c55  4 weeks ago  266 MB
ubuntu           latest   99ec81b80c55  4 weeks ago  266 MB
ubuntu           trusty   99ec81b80c55  4 weeks ago  266 MB
...

In the listed information, you can see several field information

• Which warehouse, such as ubuntu, came from?
• The tag of the mirror, such as 14.04
• Its ID number (unique)
• The time of creation
• Mirror size

Where the ID uniquely identifies the mirror, ubuntu:14.04 and ubuntu:trusty the same mirror ID indicating that they are actually the same mirror.

TAG information is used to mark different images from the same warehouse. F or ubuntu TAG release versions by TAG information, such as 10.04 12.04 12.10 13.04 14.04 on. For example, the following command specifies ubuntu:14.04 to start a container.

$ sudo docker run -t -i ubuntu:14.04 /bin/bash

If you do not specify a specific tag, the latest by default.