Opening a shell in container in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Opening an interactive shell inside a running container

You have a running Docker container named webapp. Which command opens an interactive bash shell inside it?

A docker exec -it webapp bash

B docker run -it webapp bash

C docker start -it webapp bash

D docker attach webapp bash

💡 Hint

Use docker exec to run commands inside a running container.

docker exec -it webapp bash opens an interactive bash shell inside the running container named webapp. docker run starts a new container, docker start only starts a stopped container without running commands, and docker attach connects to the main process's input/output but does not accept a command argument.

💻 Command Output

intermediate

Opening a shell in a container without bash

You want to open a shell inside a running container named db, but it does not have bash installed. Which command will open a shell using sh instead?

A docker exec -it db bash

B docker exec -it db sh

C docker run -it db sh

D docker attach db sh

💡 Hint

Try using a simpler shell like sh if bash is missing.

docker exec -it db sh opens an interactive shell using sh inside the running container named db. docker run starts a new container, and docker attach does not accept a command argument.

❓ Troubleshoot

advanced

Why does 'docker exec -it container_name bash' fail with 'exec: "bash": executable file not found'?

You run docker exec -it mycontainer bash but get the error exec: "bash": executable file not found in $PATH. What is the most likely cause?

A The container image does not have bash installed.

B The container is not running.

C You forgot to use sudo before the command.

D The Docker daemon is not running.

💡 Hint

Check what shells are available inside the container.

The error means the bash program is missing inside the container. Some minimal images only have sh or other shells. The container being stopped or Docker daemon down would cause different errors. sudo is not always required.

🔀 Workflow

advanced

Steps to open a shell in a stopped container

You have a stopped container named app. Which sequence of commands correctly opens an interactive shell inside it?

A 2,1

B 3,4

C 1,2

D 4,1

💡 Hint

You must start the container before executing commands inside it.

First, docker start app starts the stopped container. Then, docker exec -it app bash opens an interactive shell inside it. docker run creates a new container, and docker attach connects to the main process but does not start the container if stopped.

✅ Best Practice

expert

Best practice for opening a shell in a container for debugging

Which practice is best when you want to debug a running container without affecting its main process?

A Use <code>docker attach container_name</code> to connect to the main process.

B Stop the container and run <code>docker run -it container_name bash</code>.

C Restart the container with <code>docker restart container_name</code> and then open a shell.

D Use <code>docker exec -it container_name sh</code> to open a new shell session.

💡 Hint

Opening a separate shell session avoids interfering with the main process.

docker exec -it container_name sh opens a new shell inside the running container, allowing safe debugging without disturbing the main process. docker attach connects to the main process's input/output and can disrupt it. Restarting or stopping the container interrupts service.