Executing commands with docker exec - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to run a shell inside a running container named 'webapp'.

Docker

docker exec -it [1] /bin/bash

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

Awebapp

Brun

Cbuild

Dimage

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'run' or 'build' instead of the container name.

Forgetting to specify the container name.

The docker exec command requires the container name or ID to specify where to run the command. Here, 'webapp' is the container name.

2fill in blank

medium

Complete the command to list files inside the container 'db' in the '/var/log' directory.

Docker

docker exec [1] ls /var/log

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

A-d

B-it

Ccontainer

Ddb

Attempts:

3 left

💡 Hint

Common Mistakes

Using options like '-it' or '-d' instead of the container name.

Using the word 'container' instead of the actual container name.

The container name 'db' is needed to tell Docker where to run the ls command.

3fill in blank

hard

Fix the error in the command to run 'env' inside container 'app1' interactively.

Docker

docker exec [1] app1 env

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

A-it

B-d

C--rm

D-p

Attempts:

3 left

💡 Hint

Common Mistakes

Using -d which runs the command detached and does not allow interaction.

Using --rm which is for removing containers after run, not exec.

The -it option allows interactive terminal access, which is needed to run commands interactively inside the container.

4fill in blank

hard

Fill both blanks to run 'cat /etc/hosts' inside container 'backend' with a pseudo-TTY and keep STDIN open.

Docker

docker exec [1] [2] cat /etc/hosts

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

A-it

B-d

Cbackend

D--rm

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of container name and options.

Using -d which detaches and does not allow interaction.

The container name 'backend' is needed to specify where to run the command. The -it option allows interactive terminal access.

5fill in blank

hard

Fill all three blanks to run 'echo Hello' inside container 'frontend' interactively and detach after execution.

Docker

docker exec [1] [2] [3] echo Hello

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

A-it

Bfrontend

C-d

D--rm

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of options and container name.

Using --rm which is not valid for exec.

The container name is 'frontend'. The -it option allows interactive terminal, and -d runs the command in detached mode.

Practice

1. What does the docker exec command do?

easy

A. Runs a command inside a running container

B. Starts a new container from an image

C. Stops a running container

D. Builds a Docker image from a Dockerfile

Solution

1. Step 1: Understand the purpose of docker exec

   The docker exec command is used to run commands inside an already running container without stopping it.

2. Step 2: Compare with other Docker commands

   Starting a container is done with docker run, stopping with docker stop, and building images with docker build. These are different from docker exec.

3. Final Answer:

   Runs a command inside a running container -> Option A

4. Quick Check:

   docker exec = run command inside container [OK]

Hint: Remember: exec means execute inside running container [OK]

Common Mistakes:

• Confusing exec with docker run
• Thinking exec stops containers
• Mixing exec with image build commands

2. Which of the following is the correct syntax to start an interactive bash shell inside a running container named webapp?

easy

A. docker exec webapp bash -it

B. docker exec bash -it webapp

C. docker exec -ti bash webapp

D. docker exec -it webapp bash

Solution

1. Step 1: Recall the correct option order for docker exec

   The correct syntax places options like -it immediately after docker exec, then the container name, then the command.

2. Step 2: Validate each option

   docker exec -it webapp bash correctly uses docker exec -it webapp bash. Options A, B, and C have incorrect order of arguments or options.

3. Final Answer:

   docker exec -it webapp bash -> Option D

4. Quick Check:

   Options come right after exec, then container, then command [OK]

Hint: Options (-it) come right after exec, before container name [OK]

Common Mistakes:

• Placing options after container name
• Swapping container name and command
• Using wrong option order like -ti instead of -it

3. Given a running container named db, what will be the output of this command?

docker exec db ls /var/lib/mysql

medium

A. Shows an error because ls is not a valid command

B. Lists files on the host machine's /var/lib/mysql directory

C. Lists files and folders inside /var/lib/mysql in the container

D. Starts a new container named db and runs ls

Solution

1. Step 1: Understand what docker exec does with ls /var/lib/mysql

   The command runs ls /var/lib/mysql inside the running container named db, listing files in that path inside the container.

2. Step 2: Eliminate incorrect options

   ls is a valid command inside Linux containers, so no error. It does not list host files or start a new container.

3. Final Answer:

   Lists files and folders inside /var/lib/mysql in the container -> Option C

4. Quick Check:

   docker exec runs command inside container filesystem [OK]

Hint: Exec runs commands inside container, not on host [OK]

Common Mistakes:

• Thinking exec runs commands on host
• Assuming exec starts new containers
• Believing ls is invalid inside containers

4. You run docker exec webapp bash but get the error: the input device is not a TTY. What is the likely fix?

medium

A. Stop the container and restart it

B. Add the -it flags to enable interactive terminal

C. Use docker run instead of docker exec

D. Remove the bash command from the exec

Solution

1. Step 1: Understand the error about TTY

   The error means the command expects an interactive terminal but none was allocated.

2. Step 2: Fix by adding -it flags

   Adding -it allocates a pseudo-TTY and keeps stdin open, enabling interactive shells inside containers.

3. Final Answer:

   Add the -it flags to enable interactive terminal -> Option B

4. Quick Check:

   Interactive shells need -it flags [OK]

Hint: Use -it for interactive commands to avoid TTY errors [OK]

Common Mistakes:

• Ignoring the need for -it flags
• Restarting container unnecessarily
• Confusing exec with run command

5. You want to check the environment variables inside a running container named api. Which command correctly does this and shows output interactively?

hard

A. docker exec -it api env

B. docker exec env api

C. docker exec -it env api

D. docker exec api -it env

Solution

1. Step 1: Identify the need for interactive output

   To see environment variables interactively, you need to allocate a TTY and keep stdin open using -it.

2. Step 2: Check command syntax

   docker exec -it api env correctly places -it after docker exec, then container name api, then command env. Other options have wrong order or missing flags.

3. Final Answer:

   docker exec -it api env -> Option A

4. Quick Check:

   Use -it before container name for interactive commands [OK]

Hint: Place -it right after exec for interactive commands [OK]

Common Mistakes:

• Placing -it after container or command
• Omitting -it for interactive output
• Swapping command and container name