Question 1

What does the -d flag do in docker run?

Accepted Answer

The `-d` (detached) flag runs the container in the background and prints the container ID. Without `-d`, the container runs in the foreground and you see its logs in your terminal. Detached mode is typical for long-running services like web servers or databases.

Question 2

What is the difference between --rm and persistent containers?

Accepted Answer

The `--rm` flag automatically removes the container and its writable layer when it exits. This is useful for one-off tasks and keeps your system clean. Without `--rm`, stopped containers remain on disk (visible with `docker ps -a`) and must be manually removed with `docker rm`. Named containers without `--rm` can be restarted with `docker start`.

Question 3

How do port mappings work?

Accepted Answer

The `-p host:container` syntax maps a port on your host machine to a port inside the container. For example, `-p 8080:80` means requests to `localhost:8080` are forwarded to port 80 inside the container. You can map multiple ports with multiple `-p` flags. Use `127.0.0.1:8080:80` to restrict binding to localhost only.

Question 4

What restart policies are available?

Accepted Answer

Docker supports four restart policies: `no` (default) — never restart; `always` — always restart regardless of exit code; `on-failure` — restart only when container exits with non-zero status; `unless-stopped` — always restart unless explicitly stopped by the user. For production services, `unless-stopped` or `always` is recommended.

Question 5

What is the --privileged flag and when should I use it?

Accepted Answer

The `--privileged` flag gives the container almost all capabilities of the host system, including access to all devices. It disables the security isolation that containers normally provide. It is needed for containers that need to run nested Docker, modify kernel parameters, or manage hardware. Avoid it in production unless absolutely necessary as it is a significant security risk.

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