Learning term
Command — Docker fundamentals
Command defines the program and arguments run as PID 1 in a container. This card shows its role in “Docker fundamentals” and a safe diagnostic path.
Orientation
Command defines the program and arguments run as PID 1 in a container. At this level, separate purpose, input, and visible result. Place Command within Docker fundamentals before changing settings or files.
Practical use
Inspect the entrypoint and arguments when the container exits immediately with code 127. Start in a sandbox with neutral examples. Record the expected state, make one controlled change, and compare status output, application behavior, and logs.
Technical understanding
Command defines the program and arguments run as PID 1 in a container. Technically, Command connects through interfaces, configuration, state, or dependencies. Trace data from input to output and check versions, permissions, networking, storage, and resources separately.
Operations and debugging
Inspect the entrypoint and arguments when the container exits immediately with code 127. In production-like operations, use measurable signals, least privilege, reproducible configuration, and a documented rollback. Preserve evidence, isolate the cause, and verify the correction with the same test.
Exercise
Try it safely
Inspect the entrypoint and arguments when the container exits immediately with code 127. Open an isolated test environment and run “docker version && docker info”. Write down the expected output first, do not alter production data, and record one safe next diagnostic step.
docker version && docker infoQuick check
Can you explain the purpose, observable state, and most common failure source of Command — Docker fundamentals in one sentence each? Which evidence would you preserve before changing anything, and which repeated test would prove that the correction actually worked?