Copying files to and from containers in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to copy a file named app.log from your local machine to a running container named webapp.

Docker

docker cp app.log [1]:/var/log/

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

Awebapp:/var/log

Bwebapp

Cwebapp:/app

Dwebapp:/home

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to include the colon between container name and path.

Using only the container name without the destination path.

The correct syntax to copy a file into a container is docker cp source_path container_name:destination_path. Here, webapp:/var/log specifies the container and the destination folder.

2fill in blank

medium

Complete the command to copy a file named config.yaml from a container named db to your local directory /configs.

Docker

docker cp [1]:/etc/config.yaml /configs/

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

Adb

Bdb:/etc/config.yaml

Cdb:/etc

Ddb:/config.yaml

Attempts:

3 left

💡 Hint

Common Mistakes

Specifying only the container name without the file path.

Using a directory path instead of the full file path.

To copy a file from a container, specify container_name:path_to_file. Here, db:/etc/config.yaml points to the exact file inside the container.

3fill in blank

hard

Fix the error in the command that tries to copy data.csv from the container analytics to the current directory.

Docker

docker cp analytics[1]data.csv .

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

A:

B/

C:/

D::

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the colon.

Using double colons or no slash after colon.

The correct syntax requires a colon and a slash to separate the container name and the file path: container_name:/path/to/file. So analytics:/data.csv is correct.

4fill in blank

hard

Fill both blanks to copy the entire directory /app/data from the container backend to the local directory ./backup.

Docker

docker cp [1] [2]

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

Abackend:/app/data

B./backup

C/backup

Dbackend:/backup

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping source and destination.

Using incorrect paths or missing colon.

The source is the directory inside the container: backend:/app/data. The destination is the local directory: ./backup.

5fill in blank

hard

Fill all three blanks to copy the file settings.json from the local directory ./configs to the container frontend inside the path /usr/src/app/config.

Docker

docker cp [1]/[2] [3]:/usr/src/app/config/

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

A./configs

Bsettings.json

Cfrontend

D/usr/src/app

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up container name and local path.

Forgetting to include the file name in the source path.

The source is the local file path: ./configs/settings.json. The destination is the container and path: frontend:/usr/src/app/config/.

Practice

1. What does the docker cp command do?

easy

A. Copies files or folders between your computer and a Docker container

B. Copies Docker images between registries

C. Copies environment variables from a container

D. Copies container logs to a file

Solution

1. Step 1: Understand the purpose of docker cp

   The docker cp command is designed to transfer files or folders between the host machine and a Docker container.

2. Step 2: Differentiate from other Docker commands

   Other options relate to images, environment variables, or logs, which are not handled by docker cp.

3. Final Answer:

   Copies files or folders between your computer and a Docker container -> Option A

4. Quick Check:

   docker cp = copy files/folders [OK]

Hint: Remember: cp means copy files between host and container [OK]

Common Mistakes:

• Confusing docker cp with image transfer commands
• Thinking it copies logs or environment variables
• Assuming it copies container settings

2. Which of the following is the correct syntax to copy a file named app.log from your computer to a container named webapp at path /var/log/?

easy

A. docker cp app.log webapp:/var/log/

B. docker cp webapp:/var/log/ app.log

C. docker copy app.log webapp:/var/log/

D. docker cp /var/log/ app.log webapp

Solution

1. Step 1: Identify source and destination in docker cp

   The syntax is docker cp [source] [destination]. To copy from host to container, source is local file, destination is container:path.

2. Step 2: Check each option's order and command correctness

   docker cp app.log webapp:/var/log/ correctly uses docker cp app.log webapp:/var/log/. docker cp webapp:/var/log/ app.log reverses source and destination. docker copy app.log webapp:/var/log/ uses wrong command docker copy. docker cp /var/log/ app.log webapp has wrong order and extra arguments.

3. Final Answer:

   docker cp app.log webapp:/var/log/ -> Option A

4. Quick Check:

   docker cp source destination [OK]

Hint: Source first, then destination with container:path [OK]

Common Mistakes:

• Swapping source and destination paths
• Using wrong command name like docker copy
• Missing container name or colon separator

3. Given a container named db with a file /data/dump.sql, what will be the result of running docker cp db:/data/dump.sql ./backup.sql?

medium

A. Throws an error because the destination must be a directory

B. Copies the file dump.sql from the container to the current directory as backup.sql

C. Copies the file backup.sql from the current directory to the container at /data/dump.sql

D. Copies the entire /data directory from the container to ./backup.sql

Solution

1. Step 1: Analyze the command syntax

   The command copies from container db path /data/dump.sql to local path ./backup.sql. This means copying a single file from container to host with a new name.

2. Step 2: Understand the effect on local filesystem

   The file dump.sql inside the container is copied and saved locally as backup.sql in the current directory.

3. Final Answer:

   Copies the file dump.sql from the container to the current directory as backup.sql -> Option B

4. Quick Check:

   docker cp container:file localfile [OK]

Hint: Container source first, local destination second [OK]

Common Mistakes:

• Confusing source and destination order
• Assuming destination must be a directory
• Thinking it copies directories when given a file

4. You run docker cp mycontainer:/app/config.json ./config.json but get an error: no such file or directory. What is the most likely cause?

medium

A. You forgot to specify the container ID instead of name

B. The destination path ./config.json is invalid on your host

C. The file /app/config.json does not exist inside the container

D. You need to run the command inside the container shell

Solution

1. Step 1: Understand the error message

   The error "no such file or directory" usually means the source file inside the container does not exist at the specified path.

2. Step 2: Evaluate other options

   Container name or ID can be used interchangeably if correct. Destination path on host is usually valid if relative path is used. Running inside container shell is not needed for docker cp.

3. Final Answer:

   The file /app/config.json does not exist inside the container -> Option C

4. Quick Check:

   Source file missing = error [OK]

Hint: Check source file path inside container first [OK]

Common Mistakes:

• Assuming destination path causes error
• Thinking container name must be ID only
• Trying to run docker cp inside container shell

5. You want to copy a folder named logs from your host to a running container appserver at path /var/app/. Which command correctly copies the entire folder including its contents?

hard

A. docker cp logs/* appserver:/var/app/

B. docker cp logs/ appserver:/var/app/

C. docker cp logs appserver:/var/app/

D. docker cp logs appserver:/var/app/logs

Solution

1. Step 1: Understand folder copy behavior

   To copy a folder and its contents, specify the folder as source and the full destination path including the folder name if you want it placed inside the container.

2. Step 2: Analyze each option

   docker cp logs appserver:/var/app/logs copies the entire logs folder into /var/app/logs, preserving folder structure. docker cp logs/ appserver:/var/app/ with trailing slash copies contents of logs into /var/app/ but does not create logs folder inside container. docker cp logs appserver:/var/app/ copies contents of logs into /var/app/ without creating logs folder. docker cp logs/* appserver:/var/app/ copies only files inside logs, not subfolders.

3. Final Answer:

   docker cp logs appserver:/var/app/logs -> Option D

4. Quick Check:

   Include folder name in destination to copy folder [OK]

Hint: Add folder name in destination path to copy folder [OK]

Common Mistakes:

• Using trailing slash and losing folder structure
• Copying only files inside folder, not subfolders
• Not specifying full destination path including folder name