Executing commands with docker exec - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of docker exec with environment variable

What is the output of this command if the container named webapp has an environment variable APP_MODE=production set?

docker exec webapp printenv APP_MODE

Docker

docker exec webapp printenv APP_MODE

A APP_MODE

B Error: No such container: webapp

C printenv APP_MODE

D production

💡 Hint

The command prints the value of the environment variable inside the container.

The docker exec command runs printenv APP_MODE inside the webapp container, which outputs the value of the environment variable APP_MODE set to 'production'.

💻 Command Output

intermediate

Effect of docker exec with interactive shell

What happens when you run this command?

docker exec -it mycontainer /bin/bash

Docker

docker exec -it mycontainer /bin/bash

A Starts an interactive bash shell inside the running container named mycontainer

B Stops the container named mycontainer

C Shows the logs of the container named mycontainer

D Creates a new container named mycontainer

💡 Hint

The flags -i and -t are used for interactive terminal sessions.

The command opens an interactive bash shell inside the running container named mycontainer, allowing you to run commands inside it.

❓ Troubleshoot

advanced

Troubleshooting docker exec permission error

You run docker exec mycontainer ls /root and get a permission denied error. What is the most likely cause?

A The /root directory does not exist inside the container

B The container is not running

C The user inside the container does not have permission to access /root directory

D The docker daemon is not started

💡 Hint

Consider user permissions inside the container.

The /root directory is usually accessible only by the root user. If docker exec runs as a non-root user, permission is denied.

🔀 Workflow

advanced

Correct sequence to update a file inside a running container

You want to update a configuration file inside a running container named app. Which sequence of commands is correct?

A 2,1,3,4

B 1,2,3,4

C 1,3,2,4

D 4,1,2,3

💡 Hint

Copy the file first, then move it, verify, and restart the service.

First, copy the file into the container's temporary location, then move it to the correct path, verify the content, and finally restart the service to apply changes.

✅ Best Practice

expert

Best practice for running a command as root inside a container

Which docker exec command correctly runs apt-get update as root inside a container named db?

A docker exec -u root db apt-get update

B docker exec db -u root apt-get update

C docker exec db apt-get update -u root

D docker exec --user db root apt-get update

💡 Hint

The -u or --user flag must come before the container name.

The correct syntax is docker exec -u root db apt-get update. The -u flag specifies the user and must come before the container name.