50 Best Docker Interview Questions and Answers

Table of Contents

Docker Interview Questions and Answers

Also Read: How to Manage Ports in Docker

1. What is Docker Hub ?

Ans. It is a docker public registry where you can push your image to the Internet.

2. Which command is used to login to docker hub registry account ?

Ans. docker login

3. What is default permission given to .docker file in home directory ?

Ans. 0600

4. In which file docker will look for hostname for registry authentication ?

Ans. /home/user/.docker/config.json

5. Which command is used to upload the image to the docker repository ?

Ans. docker push

6. Which command is used to download the image from docker repository ?

Ans. docker pull

7. Which command is used to build the docker image ?

Ans. docker build

8. Which are the commands docker run will start at the background ?

Ans. docker create and docker start

9. How to remove all untagged images in docker ?

Ans. docker rmi $(docker images -q -f "dangling=true")

10. How to remove all containers that exited with a Non zero state ?

Ans. docker rm $(docker ps -a -q --filter 'exited!=0')

11. How to remove all the images from a docker node ?

Ans.docker rmi $(docker images -q)

12. How to remove all the containers from a docker node ?

Ans.docker rm $(docker ps -a -q)

13. How to list all the containers in your docker node ?

Ans. docker ps -a

14. How to list all the images in your system ?

Ans. docker images

15. Can we use the container in pause state ?

Ans. No

16. What is the command to pause the container ?

Ans. docker pause

17. What is the command to unpause the container ?

Ans. docker unpause

18. Which command will help in completely purging all the images and containers in your system ?

Ans. docker system prune

19. How to remove all unused images from a docker host ?

Ans. docker system prune -a

20. Where is the pause state helpful in docker ?

Ans. When you want to take a snapshot of the filesystem to create a new image.

21. What will you do when docker stop command does not help ?

Ans. I will most probably kill the container by using docker kill command.

22. What is the default value of blkio.weight cgroup attribute ?

Ans. 500

23. What is the option used to limit the IO read per sec from a device ?

Ans. --device-read-iops

24. What is the option used to limit the IO write per sec to a device ?

Ans. --device-write-iops

25. How to check out of memory error in docker node ?

Ans. docker events

26. Which command can be used to view docker process tree ?

Ans. pstree

27. Which process is used to map the networks ports between containers and docker nodes ?

Ans. Docker-Proxy Process

28. Which other tool can be used to get into docker container from server itself ?

Ans. nsenter

29. What is command to get into docker running container ?

Ans. docker exec

30. Which command is used to debug the docker container ?

Ans. docker inspect

31. What is the similar command in docker for Linux tail -f command to check the logs ?

Ans. docker logs -f

32. What is the default configuration file for dockerd server ?

Ans. /etc/docker/daemon.json

33. How to turn off the docker logging ?

Ans. By using --log-driver=none switch

34. Which docker environment variable usually contains docker hostname of a Server ?

Ans. $DOCKER_HOST

35. Which command used for inspecting virtual network in a docker ?

Ans. docker network ls

36. Which command is used for checking the network connected by docker container ?

Ans. docker inspect network

37. Which command is used for checking the history of Docker Images ?

Ans. docker history

38. Where does all the containers ID usually resides ?

Ans. /var/lib/docker/containers

39. Which file saves the docker networking configuration ?

Ans. hostconfig.json

40. How to check all the processes running inside a container ?

Ans. docker top <container_id>

41. What is the common debugging tool you can use for debugging docker processes ?

Ans. strace -p <PID>

42. How to run any specific commands when container initializes itself ?

Ans. By using ENTRYPOINT Keyword

43. How can you add any files to a container ?

Ans. By using ADD <source_location> <container_destination_location>

44. What are the few commands used in Dockerfile ?

Ans. FROM,ADD,RUN,CMD,ENTRYPOINT and ENV

45. How to run any commands inside a container ?

Ans. By using RUN <commands_to_run>

46. How to run any command at the start of the container ?

Ans. By using CMD <commands_to_be_run>

47. How can you set any environment variable inside a docker container ?

Ans. By using ENV <variable_name> <value>

48. What is the command to copy the files inside a container ?

Ans. docker cp

49. Which tool can be used for multi-container docker applications ?

Ans. docker-compose

50. Which tool can be used to create and start all services through a YAML file configuration ?