In a Dockerfile, which instruction is commonly used to produce a new layer by executing build-time commands?

In a Dockerfile, which instruction is commonly used to produce a new layer by executing build-time commands?

• A. LABEL
• B. CMD
• C. COPY
• D. RUN

Answer: (D)

Running commands during the image build is what creates a new layer that records the resulting filesystem changes. The instruction that does this is the one that executes shell commands at build time, turning the modifications into a fresh layer in the image. For example, a statement like RUN apt-get update && apt-get install -y curl runs those commands and stores the resulting changes as a new layer. Other instructions have different roles: COPY adds files and creates a layer but doesn’t execute build-time commands to modify the filesystem; LABEL adds metadata; CMD specifies what runs when a container starts, which is at runtime, not during the build. So the instruction that produces a new layer by executing build-time commands is RUN.

Running commands during the image build is what creates a new layer that records the resulting filesystem changes. The instruction that does this is the one that executes shell commands at build time, turning the modifications into a fresh layer in the image. For example, a statement like RUN apt-get update && apt-get install -y curl runs those commands and stores the resulting changes as a new layer. Other instructions have different roles: COPY adds files and creates a layer but doesn’t execute build-time commands to modify the filesystem; LABEL adds metadata; CMD specifies what runs when a container starts, which is at runtime, not during the build. So the instruction that produces a new layer by executing build-time commands is RUN.