Running containers in detached mode in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to run a Docker container in detached mode.

Docker

docker run [1] nginx

Drag options to blanks, or click blank then click option'

A-d

B-it

C--rm

D-p

Attempts:

3 left

💡 Hint

Common Mistakes

Using -it runs the container interactively, not detached.

Using --rm removes the container after it stops, unrelated to detached mode.

Using -p is for port mapping, not for detached mode.

The -d flag runs the container in detached mode, meaning it runs in the background.

2fill in blank

medium

Complete the command to run a container named 'webapp' in detached mode.

Docker

docker run [1] --name webapp nginx

Drag options to blanks, or click blank then click option'

A-it

B-p

C--rm

D-d

Attempts:

3 left

💡 Hint

Common Mistakes

Using -it runs the container interactively.

Using --rm removes the container after exit.

Using -p maps ports but does not detach.

The -d flag runs the container in detached mode, allowing it to run in the background with the given name.

3fill in blank

hard

Fix the error in the command to run a container in detached mode.

Docker

docker run nginx [1]

Drag options to blanks, or click blank then click option'

A-d

B-it

C--rm

D-p

Attempts:

3 left

💡 Hint

Common Mistakes

Placing the flag after the image name causes an error.

Using -it runs interactively, not detached.

The -d flag must come before the image name to run the container detached.

4fill in blank

hard

Fill both blanks to run a container in detached mode and map port 8080 on the host to 80 in the container.

Docker

docker run [1] -p [2]:80 nginx

Drag options to blanks, or click blank then click option'

A-d

B8080

C80

D-it

Attempts:

3 left

💡 Hint

Common Mistakes

Using -it instead of -d for detached mode.

Swapping port numbers in the mapping.

Use -d to run detached and -p 8080:80 to map host port 8080 to container port 80.

5fill in blank

hard

Fill all three blanks to run a container detached, name it 'db', and map port 3306 on the host to 3306 in the container.

Docker

docker run [1] --name [2] -p [3]:3306 mysql

Drag options to blanks, or click blank then click option'

A-d

Bdb

C3306

D-it

Attempts:

3 left

💡 Hint

Common Mistakes

Using -it instead of -d for detached mode.

Incorrect port mapping format.

Forgetting to name the container.

Use -d for detached mode, --name db to name the container, and -p 3306:3306 to map the port.

Practice

1. What does running a Docker container with the -d option do?

easy

A. Runs the container in detached mode, in the background

B. Runs the container interactively with a terminal

C. Removes the container after it stops

D. Builds a new Docker image from a Dockerfile

Solution

1. Step 1: Understand the -d option meaning

   The -d flag tells Docker to run the container in detached mode, meaning it runs in the background.

2. Step 2: Compare with other options

   Other options like interactive mode (-it) keep the container attached to the terminal, which is different from detached mode.

3. Final Answer:

   Runs the container in detached mode, in the background -> Option A

4. Quick Check:

   Detached mode = background run [OK]

Hint: Remember: -d means detach and run in background [OK]

Common Mistakes:

• Confusing -d with -it for interactive mode
• Thinking -d removes the container
• Mixing up build and run commands

2. Which of the following is the correct syntax to run a container named myapp in detached mode using the image nginx?

easy

A. docker run nginx -d --name myapp

B. docker run -d --name myapp nginx

C. docker run --detach myapp nginx

D. docker run --name myapp -it nginx

Solution

1. Step 1: Identify correct order and flags

   The correct syntax places options before the image name. The -d flag enables detached mode, and --name myapp names the container.

2. Step 2: Validate each option

   docker run -d --name myapp nginx correctly uses docker run -d --name myapp nginx. docker run --detach myapp nginx misplaces arguments, docker run nginx -d --name myapp places flags after image, and docker run --name myapp -it nginx uses interactive mode instead of detached.

3. Final Answer:

   docker run -d --name myapp nginx -> Option B

4. Quick Check:

   Options before image, -d for detached [OK]

Hint: Put all flags before the image name in docker run [OK]

Common Mistakes:

• Placing flags after the image name
• Using -it instead of -d for detached mode
• Misusing --detach instead of -d

3. What will be the output of the command docker ps after running docker run -d nginx?

medium

A. Shows the logs of the nginx container

B. Shows no containers because detached mode hides them

C. Shows an error because -d is not valid with nginx

D. Shows the running nginx container with its container ID and status

Solution

1. Step 1: Understand docker run -d nginx

   This command runs the nginx container in detached mode, so it runs in the background.

2. Step 2: Understand docker ps output

   The docker ps command lists all running containers, including those running detached. It will show the nginx container with its ID, image, and status.

3. Final Answer:

   Shows the running nginx container with its container ID and status -> Option D

4. Quick Check:

   docker ps lists running containers including detached [OK]

Hint: docker ps always lists running containers, detached or not [OK]

Common Mistakes:

• Thinking detached containers are hidden from docker ps
• Confusing docker ps with docker logs
• Assuming -d causes errors with nginx image

4. You ran docker run -d nginx but the container stopped immediately. What is the most likely reason?

medium

A. The -d flag is invalid and caused the container to stop

B. You forgot to add the -it flag for interactive mode

C. The nginx container exited because it has no foreground process

D. Docker daemon is not running

Solution

1. Step 1: Understand container lifecycle with detached mode

   Detached mode runs containers in background, but if the main process exits immediately, the container stops.

2. Step 2: Analyze nginx container behavior

   Some nginx images may exit if no foreground process runs. This causes the container to stop right after starting.

3. Final Answer:

   The nginx container exited because it has no foreground process -> Option C

4. Quick Check:

   Container stops if main process exits immediately [OK]

Hint: Detached mode won't keep container alive if main process ends [OK]

Common Mistakes:

• Assuming -d flag causes errors
• Confusing interactive mode with container lifecycle
• Not checking if Docker daemon is running

5. You want to run a container in detached mode and later check its logs. Which sequence of commands is correct?

hard

A. docker run -d --name myapp nginx; docker logs myapp

B. docker run --name myapp nginx -d; docker stop myapp

C. docker run -it --name myapp nginx; docker logs myapp

D. docker run -d nginx; docker attach myapp

Solution

1. Step 1: Run container in detached mode with a name

   Use docker run -d --name myapp nginx to start the container in background with a name for easy reference.

2. Step 2: Check logs of the running container

   Use docker logs myapp to view the logs of the named container without attaching to it.

3. Final Answer:

   docker run -d --name myapp nginx; docker logs myapp -> Option A

4. Quick Check:

   Detached run + named container + logs command [OK]

Hint: Name containers to easily check logs after detached run [OK]

Common Mistakes:

• Using -it instead of -d for detached mode
• Trying to attach instead of using logs to view output
• Placing -d after image name