Late Post

Learn how to view Docker logs to troubleshoot containers

In case you deploy containers with Docker, sooner or later you will must troubleshoot. Jack Wallen reveals you ways to take action with the logs command.

Illustration: Lisa Hornung/TechRepublic

Containers could be a difficult answer to deploy and handle. Given there are such a lot of shifting items to this puzzle, it is usually very difficult to even know the place to start when hassle strikes. Is it the host? What in regards to the community? Possibly it is the supplier? Or perhaps it is only a container that is gone awry.

After you have discovered nothing fallacious along with your host, community, or supplier, it is time to have a look at what might be most frequently the basis explanation for the issue…the container itself.

Though containers have turn into the darling of the IT ball, they’re removed from good. Issues go fallacious. And given how difficult containers are, they usually go fallacious on the very coronary heart of your deployments.

SEE: Guidelines: Server stock (TechRepublic Premium)

So what do you do? How do you troubleshoot a single container? Thankfully, the builders thought of that and added a command that means that you can test the logs of a container. Let’s learn how to make use of this useful software.

What you will want

The one factor you will must view Docker container logs is Docker deployed to a machine. It would not matter what the platform is, as long as it helps Docker. I will be demonstrating on Ubuntu Server 20.04.

With that single requisite out of the best way, let’s view these logs.

Learn how to use the Docker log command

I will deploy an NGINX container to exhibit how container logs are seen. So log into your Docker host and deploy the NGINX container with the command:

docker run --name docker-nginx -p 8080:80 -d nginx

Give it a second and you need to have a brand new NGINX container operating, named docker-nginx. Open an online browser and level it to http://SERVER:8080 (The place SERVER is the IP handle of the internet hosting server) and you need to see the NGINX welcome web page.

However for example that web page would not seem? What provides? Why is my container not operating? To search out out, we might challenge the command:

docker logs docker-nginx

Docker will instantly print out the entire log file info it has (Determine A).

Determine A


The Docker logs of our newly deployed NGINX container.

In fact, our container would not have any errors, as a result of it is operating simply high-quality. Even so, that is a number of output to comb by means of. To illustrate you solely need to view the final 5 traces from the log file. For that you might challenge the command:

docker logs docker-nginx --tail 5

Or perhaps you need to view the logs as they’re written (so you possibly can extra simply troubleshoot a container because it sends and receives knowledge). For that you’ll use the comply with possibility like so:

docker logs docker-nginx --follow

It will proceed outputting info, so you possibly can watch the logs being written in actual time (Determine B).

Determine B


Following the Docker log file for our operating docker-nginx container.

To illustrate you recognize one thing went fallacious throughout the final hour and also you need to solely view the logs which were written inside that timeframe. For that, challenge the command:

docker logs docker-nginx --since=60m

Or perhaps you recognize one thing went fallacious previous to an hour in the past. You should use the till choice to show each log file written prior with the command:

docker logs docker-nginx --until=60m

Lastly, you may need to add a couple of additional particulars to your log output, which is completed with the –details possibility:

docker logs docker-nginx --details

Between these instructions, you need to have the whole lot it is advisable to troubleshoot a selected Docker container. One factor to notice is you can substitute the Container ID for the Identify (as I’ve used above). To search out the related Container ID, challenge the command:

docker ps -a

Whenever you run the docker logs command utilizing the Container ID, you solely want to make use of the primary 4 characters of the ID, as in:

docker logs 118b --details

And that is all there may be to viewing the logs of your Docker containers.

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