Developing with Docker

Identifying images and containers

As you remember from the previous chapters, images that you want to run can be identified simply by there name, such as Ubuntu. In this case, Docker will pick the image tagged by latest by default. You can also use the tag syntax or the digest syntax:

Image[:tag]
Image[@digest]

For example, if you want to run Ubuntu tagged as version 14.04, you simply execute the command:

docker run ubuntu:14.04

The image can contain an identifier called a digest. The digest is calculated as the sha256 checksum of the image manifest, excluding the signature portion. The manifest comprises of the image's name, its tag (latest), architecture, fsLayers (a list of the image's layers, referenced by their digests), history, schema version, ...