Restarting containers in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to restart a Docker container named 'webapp'.

Docker

docker container [1] webapp

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

Arestart

Bstart

Cstop

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'stop' only stops the container without starting it again.

Using 'start' only starts a stopped container but does not restart it if running.

The restart command stops and then starts the container again.

2fill in blank

medium

Complete the command to restart all running Docker containers.

Docker

docker ps -q | xargs docker [1]

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

Arm

Bstart

Crestart

Dstop

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'stop' will only stop containers without restarting.

Using 'rm' will remove containers instead of restarting.

This command restarts all containers listed by docker ps -q, which shows container IDs.

3fill in blank

hard

Fix the error in the command to restart a container with ID 'abc123'.

Docker

docker container [1] abc123

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

Aremove

Bstart

Cstop

Drestart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' does not restart a running container.

Using 'stop' only stops the container without starting it again.

The correct command to restart a container is docker container restart.

4fill in blank

hard

Fill both blanks to restart all containers that are currently stopped.

Docker

docker ps -a -f status=[1] -q | xargs docker [2]

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

Aexited

Brestart

Crunning

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'restart' on stopped containers is valid but here we want to start only.

Filtering by 'running' will select running containers, not stopped ones.

The filter status=exited selects stopped containers, and start starts them again.

5fill in blank

hard

Fill all three blanks to restart containers with names starting with 'db'.

Docker

docker ps -a --filter name=[1] -q | xargs docker [2] [3]

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

A"^db"

Brestart

C--time=5

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' instead of 'restart' will not restart running containers.

Not using quotes around the regex filter can cause errors.

The filter name="^db" selects containers whose names start with 'db'. The restart command restarts them with a 5-second timeout.

Practice

1. What does the docker restart <container_name> command do?

easy

A. Only starts the specified container

B. Only stops the specified container

C. Deletes the specified container

D. Stops and then starts the specified container

Solution

1. Step 1: Understand the restart command

   The docker restart command is designed to stop a running container and then start it again.

2. Step 2: Compare with other commands

   Stopping only halts the container, starting only launches it, and deleting removes it. Restart does both stop and start.

3. Final Answer:

   Stops and then starts the specified container -> Option D

4. Quick Check:

   Restart = Stop + Start [OK]

Hint: Restart means stop then start container [OK]

Common Mistakes:

• Thinking restart only stops or only starts
• Confusing restart with remove or delete
• Assuming restart creates a new container

2. Which of the following is the correct syntax to restart a container named webapp?

easy

A. docker restart -c webapp

B. docker restart webapp

C. docker restart --container webapp

D. docker restart container webapp

Solution

1. Step 1: Recall the basic restart syntax

   The correct syntax is docker restart <container_name> without extra flags for container name.

2. Step 2: Evaluate the options

   Options B, C, and D add invalid flags or keywords not recognized by Docker CLI for restart.

3. Final Answer:

   docker restart webapp -> Option B

4. Quick Check:

   Simple restart command = docker restart container_name [OK]

Hint: Use 'docker restart' plus container name only [OK]

Common Mistakes:

• Adding unnecessary flags like -c or --container
• Using extra keywords after restart
• Confusing restart syntax with other commands

3. What will be the output of the command docker restart myapp if the container myapp is currently stopped?

medium

A. myapp

B. Error: Container is not running

C. Container myapp restarted successfully

D. No output

Solution

1. Step 1: Understand restart behavior on stopped container

   If the container is stopped, docker restart will start it and print the container name.

2. Step 2: Check Docker CLI output format

   The command outputs the container name on success, not a success message or error if stopped.

3. Final Answer:

   myapp -> Option A

4. Quick Check:

   Restart prints container name on success [OK]

Hint: Restart prints container name even if stopped [OK]

Common Mistakes:

• Expecting an error if container is stopped
• Expecting a success message instead of container name
• Thinking restart does nothing if container stopped

4. You run docker restart 123abc but get an error: Error: No such container: 123abc. What is the likely cause?

medium

A. Docker daemon is not running

B. The container is already running

C. The container ID or name is incorrect or does not exist

D. You need to add --force flag to restart

Solution

1. Step 1: Analyze the error message

   The error says no such container, meaning Docker cannot find a container with ID or name '123abc'.

2. Step 2: Check other options

   Running container does not cause this error, Docker daemon not running causes different errors, and --force is not a valid restart flag.

3. Final Answer:

   The container ID or name is incorrect or does not exist -> Option C

4. Quick Check:

   No such container = wrong ID/name [OK]

Hint: Check container ID/name spelling if 'No such container' error [OK]

Common Mistakes:

• Assuming container must be stopped to restart
• Trying to force restart with invalid flags
• Ignoring Docker daemon status

5. You want a container to automatically restart if it crashes or Docker restarts. Which command correctly starts a container named db with this behavior?

hard

A. docker run --restart=always db

B. docker run --restart=never db

C. docker run --restart=on-failure db

D. docker run --restart=unless-stopped db

Solution

1. Step 1: Understand restart policies

   The --restart=always policy restarts the container whenever it stops, including crashes and Docker daemon restarts.

2. Step 2: Compare other policies

   never disables restart, on-failure restarts only on errors, and unless-stopped restarts except when manually stopped.

3. Final Answer:

   docker run --restart=always db -> Option A

4. Quick Check:

   Always restart = auto restart on crash and daemon restart [OK]

Hint: Use --restart=always for auto restart on crash and reboot [OK]

Common Mistakes:

• Using --restart=never which disables restart
• Confusing on-failure with always
• Not setting restart policy at container start