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Docker Logs

When containers are running in detached mode with the -d flag, you don't see any output in your terminal, which is nice for keeping your terminal clean, but what if something goes wrong?

Enter the docker logs command.

docker logs [OPTIONS] CONTAINER
# CONTAINER can be an id or name

Assignment

Let's run the Linux alpine image in a new container in detached mode, and give it a simple command to run to generate some standard output:

docker run -d --name logdate alpine sh -c 'while true; do echo "LOGGING: $(date)"; sleep 1; done'

The sh -c 'while true; do echo "LOGGING: $(date)"; sleep 1; done' part is just a simple shell script to execute inside the container that prints the current date and time every second.

Find the ID of the running container with docker ps.
Use the docker logs command to view the logs of the container.

Notice that if you run docker logs over and over again, you will get different output. That's because you're only getting the most recent logs each time.

Add the -f flag to the docker logs command to follow the logs in real-time.
Exit the logs with Ctrl+C, then view only the most recent 5 logs with the --tail option:

docker logs --tail 5 CONTAINER

Run and submit the CLI tests, then stop and remove the container.