Opening a shell in container in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to open an interactive shell inside a running Docker container named 'myapp'.

Docker

docker exec -it myapp [1]

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

Arun

Bstop

Cstart

D/bin/bash

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'run' instead of a shell path.

Trying to start or stop the container instead of opening a shell.

The /bin/bash option opens a bash shell inside the container.

2fill in blank

medium

Complete the command to open a shell in a container with ID 'abc123' using sh shell.

Docker

docker exec -it abc123 [1]

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

A/bin/bash

Bbash

C/bin/sh

Dsh

Attempts:

3 left

💡 Hint

Common Mistakes

Using just 'sh' without the full path.

Using bash when it might not be installed.

The /bin/sh is a lightweight shell available in many containers.

3fill in blank

hard

Fix the error in the command to open a shell in container 'webapp'.

Docker

docker exec -it [1] /bin/bash

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

Awebapp

B-webapp

Cwebapp/

Dweb app

Attempts:

3 left

💡 Hint

Common Mistakes

Adding dashes or slashes to the container name.

Using spaces in the container name.

The container name should be exactly 'webapp' without extra characters or spaces.

4fill in blank

hard

Fill both blanks to open a shell in container 'db' and keep the session interactive.

Docker

docker [1] -it [2] /bin/bash

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

Aexec

Brun

Cdb

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'run' which starts a new container instead of exec.

Using 'start' which does not open a shell.

docker exec runs a command in a running container, and db is the container name.

5fill in blank

hard

Fill all three blanks to open an interactive shell in container 'app1' using sh shell.

Docker

docker [1] [2] app1 [3]

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

Aexec

B-it

C/bin/sh

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'run' instead of 'exec'.

Forgetting the '-it' flags.

Using shell name without full path.

docker exec -it app1 /bin/sh opens an interactive shell inside the running container named 'app1'.

Practice

1. What is the main purpose of the command docker exec -it <container> /bin/bash?

easy

A. To stop a running container

B. To start a new container from an image

C. To open an interactive shell inside a running container

D. To build a Docker image

Solution

1. Step 1: Understand the command components

   The command uses docker exec to run a command inside a running container. The -it flags make the session interactive and allocate a terminal.

2. Step 2: Identify the command's effect

   Using /bin/bash opens a shell inside the container, allowing direct interaction.

3. Final Answer:

   To open an interactive shell inside a running container -> Option C

4. Quick Check:

   docker exec -it container /bin/bash = open shell [OK]

Hint: Remember exec + -it + shell opens container shell [OK]

Common Mistakes:

• Confusing exec with docker run
• Forgetting the -it flags for interactivity
• Trying to open shell in a stopped container

2. Which of the following is the correct syntax to open a shell inside a running Docker container named webapp?

easy

A. docker exec -it webapp /bin/sh

B. docker start -it webapp /bin/sh

C. docker run -it webapp /bin/sh

D. docker exec webapp -it /bin/sh

Solution

1. Step 1: Recall the correct order of docker exec flags

   The -it flags must come immediately after docker exec and before the container name.

2. Step 2: Check the command structure

   The correct syntax is docker exec -it <container> <shell>. docker exec -it webapp /bin/sh matches this exactly.

3. Final Answer:

   docker exec -it webapp /bin/sh -> Option A

4. Quick Check:

   Flags -it come before container name [OK]

Hint: Flags -it always come right after exec command [OK]

Common Mistakes:

• Placing -it after container name
• Using docker run instead of exec
• Using docker start with shell command

3. Given a running container named db, what will be the output of the command docker exec -it db /bin/false?

medium

A. The command exits immediately with no shell opened

B. Error: container not found

C. An interactive shell opens inside the container

D. The container stops running

Solution

1. Step 1: Understand the command /bin/false

   The command /bin/false is a program that immediately exits with a failure status and does not open a shell.

2. Step 2: Predict the command behavior inside the container

   Running docker exec -it db /bin/false will run /bin/false inside the container, which exits immediately without opening a shell.

3. Final Answer:

   The command exits immediately with no shell opened -> Option A

4. Quick Check:

   /bin/false exits immediately, no shell [OK]

Hint: Commands like /bin/false exit immediately, no shell [OK]

Common Mistakes:

• Expecting a shell to open
• Confusing container not found error
• Thinking container stops after exec

4. You try to open a shell inside a running container with docker exec -it mycontainer /bin/bash but get the error: OCI runtime exec failed: exec failed: container_linux.go:xxx: exec: "/bin/bash": stat /bin/bash: no such file or directory. What is the best way to fix this?

medium

A. Restart the Docker daemon

B. Use /bin/sh instead of /bin/bash

C. Rebuild the container image

D. Stop and remove the container

Solution

1. Step 1: Analyze the error message

   The error says /bin/bash does not exist inside the container, so the shell is missing.

2. Step 2: Choose an alternative shell

   Many containers have /bin/sh instead of /bin/bash. Using /bin/sh usually works.

3. Final Answer:

   Use /bin/sh instead of /bin/bash -> Option B

4. Quick Check:

   Use available shell like /bin/sh if /bin/bash missing [OK]

Hint: Try /bin/sh if /bin/bash not found inside container [OK]

Common Mistakes:

• Restarting Docker daemon unnecessarily
• Rebuilding image without checking shell availability
• Removing container without trying alternative shells

5. You want to open a shell inside a running container named app but it does not have /bin/bash or /bin/sh. Which command can you try to open a shell if ash is installed inside the container?

hard

A. docker exec -it app /bin/zsh

B. docker exec -it app /bin/bash

C. docker exec -it app /bin/sh

D. docker exec -it app /bin/ash

Solution

1. Step 1: Identify available shells inside container

   If /bin/bash and /bin/sh are missing, but ash is installed, you can use /bin/ash to open a shell.

2. Step 2: Use docker exec with the correct shell path

   The command docker exec -it app /bin/ash opens an interactive shell using ash inside the container.

3. Final Answer:

   docker exec -it app /bin/ash -> Option D

4. Quick Check:

   Use shell installed inside container, e.g. /bin/ash [OK]

Hint: Try shells like /bin/ash if bash and sh missing [OK]

Common Mistakes:

• Assuming bash or sh always exist
• Using wrong shell path
• Not checking installed shells inside container