What does the command 'docker build --no-cache' do?

The command 'docker build --no-cache' is used to build a Docker image without utilizing any cached layers from previous builds. Docker generally caches the layers of images to speed up the build process, allowing for faster builds if no changes have been made to the underlying files or the Dockerfile. However, there are times when you want to ensure that every layer is built fresh, either to incorporate updates in the base images or to guarantee that your build reflects the most current state of your files.

By using the --no-cache option, the build process disregards the cache and re-executes all steps defined in the Dockerfile, creating a new image from scratch. This can be especially useful when changes have been made that might affect the current build or to troubleshoot build issues by ensuring that no stale data is being used.

This understanding directly informs why the other options are not correct. Choices that imply the use of cached layers or suggest the updating or removal of existing images do not align with the function of the --no-cache option, which is strictly about bypassing the cache during the build process.