Docker logs for troubleshooting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the docker logs command?

The docker logs command shows the output (logs) of a running or stopped container. It helps to see what happened inside the container for troubleshooting.

beginner

How do you view the last 10 lines of logs from a Docker container named webapp?

Use the command docker logs --tail 10 webapp. It shows only the last 10 lines of the container's logs.

beginner

What does the -f or --follow option do in docker logs?

The -f option streams the logs live, like watching a live feed. It shows new log lines as they appear in real time.

intermediate

How can you view logs with timestamps using docker logs?

Add the --timestamps option to the command, like docker logs --timestamps container_name. This shows when each log line was created.

beginner

Why is checking Docker logs important for troubleshooting?

Logs show what the container is doing or errors it encounters. They help find problems like crashes, misconfigurations, or missing files.

Which command shows live, real-time logs of a Docker container named app?

A docker logs -f app

B docker logs --tail 5 app

C docker ps app

D docker start app

The -f option streams logs live. So docker logs -f app shows real-time logs.

How do you limit the output to the last 20 lines of logs from a container?

A docker logs --tail 20 container

B docker logs --head 20 container

C docker logs --limit 20 container

D docker logs --last 20 container

The --tail option limits output to the last N lines.

What does the docker logs command show?

A Docker image details

B List of running containers

C Docker system info

D Output and errors from a container

It shows the container's output and error messages for troubleshooting.

Which option adds timestamps to each log line in docker logs?

A --logtime

B --time

C --timestamps

D --date

The --timestamps option shows when each log line was created.

If a container crashes, what is the best first step to find out why?

A Restart Docker service

B Check the container logs with <code>docker logs</code>

C Remove the container

D Pull the image again

Checking logs helps understand the cause of the crash.

Explain how to use docker logs to troubleshoot a container that is not working as expected.

Think about how logs show what happened inside the container.

Describe the difference between viewing all logs and following logs live in Docker.

Compare static snapshot vs live feed.