If the image does not exist locally, what will Docker do when you run a container?

If the image does not exist locally, what will Docker do when you run a container?

• A. Pauses until the image is available
• B. Pulls the image from the registry
• C. Ignores and fails to run
• D. Uses a local placeholder

Answer: (B)

When you run a container and the image isn’t present on your machine, Docker will automatically fetch that image from the registry before starting the container. This means it pulls the image layers you specified (name and tag) from the configured registry, caches them locally, and then uses the downloaded image to instantiate and run the container. If the network is available and the image exists in the registry, this pull happens seamlessly so you can proceed with the run. If there’s no network or the image isn’t in the registry, the run will fail with an error. So, the behavior isn’t to pause, ignore, or use a placeholder; it’s to fetch the image from the registry and then run. A handy tip: you can pre-pull the image with docker pull to avoid any delay at run time.

When you run a container and the image isn’t present on your machine, Docker will automatically fetch that image from the registry before starting the container. This means it pulls the image layers you specified (name and tag) from the configured registry, caches them locally, and then uses the downloaded image to instantiate and run the container. If the network is available and the image exists in the registry, this pull happens seamlessly so you can proceed with the run. If there’s no network or the image isn’t in the registry, the run will fail with an error. So, the behavior isn’t to pause, ignore, or use a placeholder; it’s to fetch the image from the registry and then run. A handy tip: you can pre-pull the image with docker pull to avoid any delay at run time.