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[Practice] Docker command

1. Normal installation confirmation​

docker run hello-world

If installed correctly, you should be able to see the following message.

Hello from Docker!
This message shows that your installation appears to be working correctly.
....

(For ubuntu) If you want to use without sudo, please refer to the following site.

2. Docker Pull​

Docker pull is a command to download Docker images from a Docker image registry (a repository where Docker images are stored and shared).

You can check the arguments available in docker pull using the command below.

docker pull --help

If performed normally, it prints out as follows.

Usage:  docker pull [OPTIONS] NAME[:TAG|@DIGEST]

Pull an image or a repository from a registry

Options:
  -a, --all-tags                Download all tagged images in the repository
      --disable-content-trust   Skip image verification (default true)
      --platform string         Set platform if server is multi-platform capable
  -q, --quiet                   Suppress verbose output

It can be seen here that docker pull takes two types of arguments.

  1. [OPTIONS]
  2. NAME[:TAG|@DIGEST]

In order to use the -a and -q options from help, they must be used before the NAME. Let's try and pull the ubuntu:18.04 image directly.

docker pull ubuntu:18.04

If interpreted correctly, the command means to pull an image with the tag 18.04 from an image named ubuntu.

If performed successfully, it will produce an output similar to the following.

18.04: Pulling from library/ubuntu
20d796c36622: Pull complete 
Digest: sha256:42cd9143b6060261187a72716906187294b8b66653b50d70bc7a90ccade5c984
Status: Downloaded newer image for ubuntu:18.04
docker.io/library/ubuntu:18.04

If you perform the above command, you will download the image called 'ubuntu:18.04' from a registry named docker.io/library to your laptop.

  • Note that
    • in the future, if you need to get a docker image from a certain private registry instead of docker.io or public docker hub, you can use docker login to point to the certain registry, then use docker pull. Alternatively, you can set up an insecure registry.
    • Also note that docker save and docker load commands are available to store and share docker images in the form of .tar file in an intranet.

3. Docker images​

This is the command to list the Docker images that exist locally.

docker images --help

The arguments available for use in docker images are as follows.

Usage:  docker images [OPTIONS] [REPOSITORY[:TAG]]

List images

Options:
  -a, --all             Show all images (default hides intermediate images)
      --digests         Show digests
  -f, --filter filter   Filter output based on conditions provided
      --format string   Pretty-print images using a Go template
      --no-trunc        Don't truncate output
  -q, --quiet           Only show image IDs

Let's try executing the command below directly.

docker images

If you install Docker and proceed with this practice, it will output something similar to this.

REPOSITORY   TAG       IMAGE ID       CREATED      SIZE
ubuntu       18.04     29e70752d7b2   2 days ago   56.7MB

If you use the -q argument among the possible arguments, only the IMAGE ID will be printed.

docker images -q
29e70752d7b2

4. Docker ps​

Command to output the list of currently running Docker containers.

docker ps --help

Use the following arguments can be used with 'docker ps':

Usage:  docker ps [OPTIONS]

List containers

Options:
  -a, --all             Show all containers (default shows just running)
  -f, --filter filter   Filter output based on conditions provided
      --format string   Pretty-print containers using a Go template
  -n, --last int        Show n last created containers (includes all states) (default -1)
  -l, --latest          Show the latest created container (includes all states)
      --no-trunc        Don't truncate output
  -q, --quiet           Only display container IDs
  -s, --size            Display total file sizes

Let's try running the command below directly.

docker ps

If there are no currently running containers, it will be as follows.

CONTAINER ID   IMAGE     COMMAND   CREATED   STATUS    PORTS     NAMES

If there is a container running, it will look similar to this.

CONTAINER ID   IMAGE     COMMAND        CREATED          STATUS          PORTS     NAMES
c1e8f5e89d8d   ubuntu    "sleep 3600"   13 seconds ago   Up 12 seconds             trusting_newton

5. Docker run​

Command to run a Docker container.

docker run --help

The command to run docker run is as follows.

Usage:  docker run [OPTIONS] IMAGE [COMMAND] [ARG...]

Run a command in a new container

What we need to confirm here is that the docker run command takes three types of arguments.

  1. [OPTIONS]
  2. [COMMAND]
  3. [ARG...]

Let's try running a docker container ourselves.

## Usage:  docker run [OPTIONS] IMAGE [COMMAND] [ARG...]
docker run -it --name demo1 ubuntu:18.04 /bin/bash
  • -it: Combination of -i and -t options
    • Runs the container and connects it to an interactive terminal
  • --name: Assigns a name to the container for easier identification instead of using the container ID
  • /bin/bash: Specifies the command to be executed in the container upon startup, where /bin/bash opens a bash shell.

After running the command, you can exit the container by using the exit command.

When you enter the previously learned docker ps command, the following output will be displayed.

CONTAINER ID   IMAGE     COMMAND   CREATED   STATUS    PORTS     NAMES

It was said that the container being executed was coming out, but for some reason the container that was just executed does not appear. The reason is that docker ps shows the currently running containers by default. If you want to see the stopped containers too, you must give the -a option.

docker ps -a

Then the list of terminated containers will also be displayed.

CONTAINER ID   IMAGE          COMMAND       CREATED         STATUS                     PORTS     NAMES
4c1aa74a382a   ubuntu:18.04   "/bin/bash"   2 minutes ago   Exited (0) 2 minutes ago             demo1

6. Docker exec​

Docker exec is a command that is used to issue commands or access the inside of a Docker container.

docker exec --help

For example, let's try running the following command.

docker run -d --name demo2 ubuntu:18.04 sleep 3600

Here, the -d option is a command that allows the Docker container to run in the background so that even if the connection ends to the container, it continues to run.

Use docker ps to check if it is currently running.

It can be confirmed that it is running as follows.

CONTAINER ID   IMAGE          COMMAND        CREATED         STATUS         PORTS     NAMES
fc88a83e90f0   ubuntu:18.04   "sleep 3600"   4 seconds ago   Up 3 seconds             demo2

Now let's connect to the running docker container through the docker exec command.

docker exec -it demo2 /bin/bash

This is the same as the previous docker run command, allowing you to access the inside of the container.

You can exit using exit.

7. Docker logs​

docker logs --help

I will have the following container be executed.

docker run --name demo3 -d busybox sh -c "while true; do $(echo date); sleep 1; done"

By using the above command, we have set up a busybox container named "test" as a Docker container in the background and printed the current time once every second.

Now let's check the log with the command below.

docker logs demo3

If performed normally, it will be similar to below.

Sun Mar  6 11:06:49 UTC 2022
Sun Mar  6 11:06:50 UTC 2022
Sun Mar  6 11:06:51 UTC 2022
Sun Mar  6 11:06:52 UTC 2022
Sun Mar  6 11:06:53 UTC 2022
Sun Mar  6 11:06:54 UTC 2022

However, if used this way, you can only check the logs taken so far.
In this case, you can use the -f option to keep watching and outputting.

docker logs demo3 -f

8. Docker stop​

Command to stop a running Docker container.

docker stop --help

Through docker ps, you can check the containers currently running, as follows.

CONTAINER ID   IMAGE          COMMAND                  CREATED              STATUS              PORTS     NAMES
730391669c39   busybox        "sh -c 'while true; …"   About a minute ago   Up About a minute             demo3
fc88a83e90f0   ubuntu:18.04   "sleep 3600"             4 minutes ago        Up 4 minutes                  demo2

Now let's try to stop Docker with docker stop.

docker stop demo2

After executing, type docker ps again.

CONTAINER ID   IMAGE     COMMAND                  CREATED         STATUS         PORTS     NAMES
730391669c39   busybox   "sh -c 'while true; …"   2 minutes ago   Up 2 minutes             demo3

Comparing with the above result, you can see that the demo2 container has disappeared from the list of currently running containers. The rest of the containers will also be stopped.

docker stop demo3

Docker rm: Command to delete a Docker container.

docker rm --help

Docker containers are in a stopped state by default. That's why you can see stopped containers using docker ps -a. But why do we have to delete the stopped containers?
Even when stopped, the data used in the Docker remains in the container. So you can restart the container through restarting. But this process will use disk. So in order to delete the containers that are not used at all, we should use the docker rm command.

First, let's check the current containers.

docker ps -a

There are three containers as follows.

CONTAINER ID   IMAGE          COMMAND                  CREATED          STATUS                            PORTS     NAMES
730391669c39   busybox        "sh -c 'while true; …"   4 minutes ago    Exited (137) About a minute ago             demo3
fc88a83e90f0   ubuntu:18.04   "sleep 3600"             7 minutes ago    Exited (137) 2 minutes ago                  demo2
4c1aa74a382a   ubuntu:18.04   "/bin/bash"              10 minutes ago   Exited (0) 10 minutes ago                   demo1

Let's try to delete the 'demo3' container through the following command.

docker rm demo3

The command docker ps -a reduced it to two lines as follows.

CONTAINER ID   IMAGE          COMMAND        CREATED          STATUS                       PORTS     NAMES
fc88a83e90f0   ubuntu:18.04   "sleep 3600"   13 minutes ago   Exited (137) 8 minutes ago             demo2
4c1aa74a382a   ubuntu:18.04   "/bin/bash"    16 minutes ago   Exited (0) 16 minutes ago              demo1

Delete the remaining containers as well.

docker rm demo2
docker rm demo1

10. Docker rmi​

Command to delete a Docker image.

docker rmi --help

Use the following commands to check which images are currently on the local.

docker images

The following is output.

REPOSITORY   TAG       IMAGE ID       CREATED        SIZE
busybox      latest    a8440bba1bc0   32 hours ago   1.41MB
ubuntu       18.04     29e70752d7b2   2 days ago     56.7MB

I will try to delete the busybox image.

docker rmi busybox

If you type docker images again, the following will appear.

REPOSITORY   TAG       IMAGE ID       CREATED        SIZE
ubuntu       18.04     29e70752d7b2   2 days ago     56.7MB

References​