Debugging volume mount issues in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to mount a local directory /data to /app/data inside the container.

Docker

docker run -v [1]:/app/data myimage

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

A/data

B/app/data

C/data/app

D/app

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the local and container paths.

Using a container path as the local path.

The local directory /data should be mounted to /app/data inside the container using -v /data:/app/data.

2fill in blank

medium

Complete the command to run a container with a read-only volume mount of /config directory.

Docker

docker run -v /config:/app/config:[1] myimage

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

Areadwrite

Bro

Crw

Dreadonly

Attempts:

3 left

💡 Hint

Common Mistakes

Using readonly instead of ro.

Forgetting the colon before the option.

The :ro option mounts the volume as read-only inside the container.

3fill in blank

hard

Fix the error in the command to mount a host directory /var/logs to /logs inside the container.

Docker

docker run -v [1] myimage

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

A/var/logs

B/logs:/var/logs

C/var:/logs

D/var/logs:/logs

Attempts:

3 left

💡 Hint

Common Mistakes

Missing the colon separator.

Swapping host and container paths.

The correct syntax for volume mount is -v host_path:container_path. Here, /var/logs is the host path and /logs is the container path.

4fill in blank

hard

Fill both blanks to create a volume mount that maps /home/user/data on the host to /data in the container with read-write access.

Docker

docker run -v [1]:[2] myimage

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

A/home/user/data

B/data

Crw

Dro

Attempts:

3 left

💡 Hint

Common Mistakes

Adding read-write option explicitly when not needed.

Swapping the host and container paths.

The volume mount syntax is -v host_path:container_path. Read-write is default, so no extra option is needed.

5fill in blank

hard

Fill all three blanks to create a volume mount with /opt/config on the host mapped to /app/config in the container as read-only.

Docker

docker run -v [1]:[2]:[3] myimage

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

A/opt/config

B/app/config

Cro

Drw

Attempts:

3 left

💡 Hint

Common Mistakes

Using rw instead of ro for read-only mount.

Swapping host and container paths.

The correct volume mount is -v /opt/config:/app/config:ro to make it read-only inside the container.

Practice

1. What is the main purpose of using volume mounts in Docker?

easy

A. To share files between the host machine and the container

B. To increase the container's CPU usage

C. To change the container's network settings

D. To update the Docker engine version

Solution

1. Step 1: Understand volume mounts

   Volume mounts allow sharing files or folders between your computer (host) and the Docker container.

2. Step 2: Identify the purpose

   This sharing helps containers access or save data on the host, making data persistent or accessible.

3. Final Answer:

   To share files between the host machine and the container -> Option A

4. Quick Check:

   Volume mounts = file sharing [OK]

Hint: Volume mounts connect host and container files [OK]

Common Mistakes:

• Confusing volume mounts with CPU or network settings
• Thinking volume mounts update Docker itself
• Assuming volume mounts only work inside containers

2. Which of the following is the correct syntax to mount a host folder /data to a container folder /app/data using docker run?

easy

A. docker run --mount /data:/app/data image_name

B. docker run -v /app/data:/data image_name

C. docker run -v /data:/app/data image_name

D. docker run -volume /data:/app/data image_name

Solution

1. Step 1: Recall volume mount syntax

   The correct syntax uses -v host_path:container_path to mount volumes.

2. Step 2: Match paths correctly

   The host folder /data should be before the colon, and container folder /app/data after.

3. Final Answer:

   docker run -v /data:/app/data image_name -> Option C

4. Quick Check:

   Host path before colon, container path after [OK]

Hint: Use -v host_path:container_path exactly [OK]

Common Mistakes:

• Swapping host and container paths
• Using incorrect flags like --mount without full syntax
• Typing -volume instead of -v

3. You run this command:
docker run -v /host/data:/container/data busybox ls /container/data
But the output is empty even though /host/data has files. What is the likely cause?

medium

A. The host path /host/data does not exist or is empty

B. The container image busybox does not support volume mounts

C. The container path /container/data is incorrect

D. The Docker daemon is not running

Solution

1. Step 1: Check host path existence

   If the host folder /host/data does not exist or is empty, the container will see nothing.

2. Step 2: Confirm container path and image

   The container path and busybox image support volume mounts, so they are unlikely the issue.

3. Final Answer:

   The host path /host/data does not exist or is empty -> Option A

4. Quick Check:

   Empty mount means host folder missing or empty [OK]

Hint: Check host folder exists and has files [OK]

Common Mistakes:

• Blaming the container image for mount issues
• Assuming container path must exist before mount
• Ignoring host folder permissions or existence

4. You tried to mount a folder with docker run -v /host/folder:/container/folder but got a permission denied error inside the container. What should you check first?

medium

A. If the Docker image supports the mounted folder

B. If the Docker CLI version is up to date

C. If the container folder path is a valid Linux path

D. If the host folder has correct read/write permissions

Solution

1. Step 1: Understand permission errors

   Permission denied usually means the container user cannot access the host folder due to host permissions.

2. Step 2: Verify host folder permissions

   Check if the host folder allows read/write access for Docker or the container user.

3. Final Answer:

   If the host folder has correct read/write permissions -> Option D

4. Quick Check:

   Permission denied = check host folder permissions [OK]

Hint: Check host folder permissions first on errors [OK]

Common Mistakes:

• Assuming container image causes permission errors
• Ignoring host file system permissions
• Updating Docker CLI instead of fixing permissions

5. You want to mount a host folder /data into a container at /app/data but only want the container to read files, not write. Which command correctly sets a read-only volume mount?

hard

A. docker run -v /data:/app/data:rw image_name

B. docker run -v /data:/app/data:ro image_name

C. docker run -v /data:/app/data:read image_name

D. docker run -v /data:/app/data:readonly image_name

Solution

1. Step 1: Recall volume mount options

   Docker uses :ro to mark a volume as read-only and :rw for read-write (default).

2. Step 2: Identify correct option

   Only :ro is valid for read-only; others like :read or :readonly are invalid.

3. Final Answer:

   docker run -v /data:/app/data:ro image_name -> Option B

4. Quick Check:

   Use :ro suffix for read-only mounts [OK]

Hint: Add :ro suffix for read-only mounts [OK]

Common Mistakes:

• Using :rw or invalid suffixes for read-only
• Forgetting the colon before options
• Assuming read-only is default