To see what’s going on within the container, you can use the docker logs command. But before using that, we need to know the container’s ID or name to see the container’s logs.
To get a list of containers running within the host, run the following command
| $ docker ps | ||||||
| CONTAINER ID | IMAGE | COMMAND | CREATED | STATUS | PORTS | NAMES |
| beb5dfd529c9 | nginx:1.18.0 | “/docker- | 2 minutes ago | Up 2 minutes | 80/tcp | fervent_ |
| entrypoint.…” | shockley |
The preceding command lists the NGINX container that we just started. Unless you specify a particular name for your container, Docker allocates a random name to it. In this case, it has called it fervent_ shockley. It also assigns every container a unique container ID, such as beb5dfd529c9.
You can use the container ID or the container name to interact with the container to list the logs. Let’s use the container ID this time:
$ docker logs beb5dfd529c9
/docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform
configuration
…
/docker-entrypoint.sh: Configuration complete; ready for start up
As you can see, it prints a similar log output as it did when we ran it in the foreground.
Practically speaking, you will use docker logs 90% of the time unless you need to debug something with BusyBox. BusyBox is a lightweight shell container that can help you troubleshoot and debug issues with your container – mostly network issues.
Let’s make BusyBox echo Hello World! for us:
$ docker run busybox echo ‘Hello World!’
Unable to find image ‘busybox:latest’ locally
latest: Pulling from library/busybox
325d69979d33: Pull complete
Digest: sha256:560af6915bfc8d7630e50e212e08242d37b63bd5c1ccf9bd4acccf116e262d5b
Status: Downloaded newer image for busybox:latest
Hello World!
As we can see, Docker pulls the latest busybox image from Docker Hub and runs the echo ‘Hello World’ command.
You can also use BusyBox in interactive mode by using the -it flag, which will help you run a series of commands on the BusyBox shell. It is also a good idea to add an –rm flag to it to tell Docker to clean up the containers once we have exited from the shell, something like this:
$ docker run -it –rm busybox /bin/sh
- # echo ‘Hello world!’ Hello world!
- # wget http://example.com
Connecting to example.com (93.184.216.34:80)
saving to ‘index.html’
index.html 100% |***********************************
****| 1256 0:00:00 ETA
‘index.html’ saved
/ # exit
Upon listing all the containers, we do not see the busybox container in there:
| $ docker ps -a | ||||||
| CONTAINER ID | IMAGE | COMMAND | CREATED | STATUS | PORTS | NAMES |
| beb5dfd529c9 | nginx: | “/docker- | 17 minutes | Up 17 | 80/tcp | fervent_ |
| 1.18.0 | entrypoint.…” | ago | minutes | shockley |
There are various other flags that you can use with your containers, each serving a specific purpose.
Let’s look at a few common ones.