 Container image

A container image packages a filesystem description and execution configuration used to create software containers. It contains such things as application files, libraries and a default command. Image layers and content identifiers permit sharing unchanged content; a running container adds execution state and usually a separate writable layer.^[ref]

For example, two containers can start from the same image while receiving different input files and environment settings. Their results need not match merely because their image matches. A container image digest identifies particular image content, while a movable tag can later refer to a different image. Most containers share a host kernel, so an image is not necessarily a complete guest operating-system installation. Reproducing a calculation also requires its inputs, configuration and compatible host facilities.