Linux+ V8 Container Runtime Troubleshooting

1. A container cannot write to a mounted volume. Which permission issue is most likely?

Container user UID doesn't match host directory owner

Volume is read-only in Dockerfile

Docker daemon lacks execute permission

Mount point doesn't exist on host

2. A container fails due to missing environment variables. Which method permanently sets these in the image?

ENV instruction in Dockerfile

Run 'docker set-env' command

-e flag at container startup

Modify /etc/environment inside container

3. Which command displays the differences between a container's file system and its base image?

Docker diff

Docker compare

Docker inspect

Docker changes

4. A container process becomes a zombie and won't terminate. What is the root cause?

Parent process doesn't handle SIGCHLD signal

Container lacks memory

Docker daemon stopped

Image is corrupted

5. When multiple containers share the host network namespace, which isolation is lost?

Process isolation

Network interface and port isolation

File system isolation

User namespace isolation

6. A container image exceeds available disk space during 'docker pull'. Where are downloaded layers stored by default?

/tmp/docker

/var/lib/docker

/home/docker

/opt/docker/images

7. The Docker daemon fails to start after a system update. Which log file contains daemon startup errors?

/var/log/docker/daemon.log

Journalctl or systemd logs

/etc/docker/config.json

/var/log/syslog only

8. A container port is exposed in Dockerfile but traffic cannot reach it. What must be explicitly done at runtime?

Run 'docker enable-port' command

Use -p flag to map host to container port

Modify iptables manually

Restart the Docker daemon

9. What is the default logging driver in Docker when no alternative is specified?

Splunk

Json-file

Syslog

Awslogs

10. Which tool provides detailed resource usage metrics for running containers in real-time?

Docker stats

Docker top

Docker events

Docker history

11. A Docker container fails to start with the error 'OCI runtime create failed'. Which component is most likely causing this issue?

Docker daemon configuration

Container image layers

Kernel or cgroup settings

Network bridge configuration

12. What does the HEALTHCHECK instruction in a Dockerfile define?

Memory limits for the container

Periodic checks to verify container is functioning

Security scanning rules

Network port exposure

13. When a container exits immediately, where should you check for initialization error messages?

/var/log/docker.log

Docker logs output

Dmesg kernel log

/var/log/containers/

14. A container image layer is corrupted. Which command rebuilds the image from source?

Docker pull

Docker build

Docker commit

Docker load

15. Which Linux kernel feature restricts container file system and process access?

Namespaces

Cgroups

SELinux

AppArmor

16. When inspecting container logs with 'docker logs', no output appears despite the container running. What is a likely cause?

Logs are stored in a separate volume

Application writes to file instead of stdout/stderr

Docker daemon requires restart

Container lacks read permissions

17. A container cannot resolve DNS names. Which file inside the container determines DNS resolver configuration?

/etc/hosts

/etc/resolv.conf

/etc/hostname

/etc/network/interfaces

18. What is the primary purpose of the containerd daemon in modern Linux container environments?

Manage high-level container API

Handle low-level runtime operations and OCI compliance

Manage Docker images exclusively

Provide network isolation only

19. A container consumes excessive CPU despite low application load. Which cgroup subsystem should you examine first?

Memory

Cpuacct

Blkio

Devices

20. When troubleshooting container networking, which command displays the internal IP address and network mode of a running container?