JIYIK CN >

This article will demonstrate how to enter the Docker container shell using multiple methods.

Use docker execto enter the Docker container's shell

We need to have a container up and running to use this command. We can check the status of the container in the system using the following command.

docker ps -a

CONTAINER ID   IMAGE     COMMAND                  CREATED      STATUS                    PORTS     NAMES
38086474cb6c   debian    "bash"                   2 days ago   Exited (0) 2 days ago               epic_jackson
1c955bac1a84   ubuntu    "bash"                   2 days ago   Exited (0) 2 days ago               musing_morse
1296f9b9d330   nginx     "/docker-entrypoint.…"   2 days ago   Exited (255) 2 days ago   80/tcp    distracted_napier

If we don't have a container running, we can easily create one. We will use rabbitmqa base image to set up a container.

Before creating the container, we will first docker pullpull the base image from the registry using the command as shown below.

$ docker run -d rabbitmq

Output:

Dcad9f270643802092ab525796897c357026767863dade831e8c7d7d82c45712

Now, we should have a running container. Once again, we can confirm using docker psthe command.

$ docker ps -a

Output:

CONTAINER ID   IMAGE      COMMAND                  CREATED              STATUS          PORTS                                                 NAMES
dcad9f270643   rabbitmq   "docker-entrypoint.s…"   About a minute ago   Up 57 seconds   4369/tcp, 5671-5672/tcp, 15691-15692/tcp, 25672/tcp   inspiring_moore

We will use the command -itnext to the tag docker execto enter the container and interact with the files or perform some debugging.

execThe command will allow us to execute commands in a running container, while -itthe tag will allow us to open the container interactively.

Finally, shthe command will open a basic shell prompt to run our commands in the container.

isaactonyloi@DESKTOP-HV44HT6:~$ docker exec -it dcad9f270643 sh
#

Now that we are inside the Docker container, we can run various commands in the container. Type exitthe command and press enter from this mode to return to the main terminal.

Use docker container attachto enter the Docker container's shell

We can also docker container attachconnect to a running container using the command. This allows us to attach the terminal output, input, and error streams to a running container using the container's ID.

We can then run various commands, accept input, and debug the specified container. As mentioned before, we need a running container to attach our output, input, and error streams.

To do this, we will use docker ps, as shown below. We are still using the container from the previous section rabbitmq.

$ docker ps -a

Output:

CONTAINER ID   IMAGE      COMMAND                  CREATED          STATUS          PORTS                                                 NAMES
dcad9f270643   rabbitmq   "docker-entrypoint.s…"   39 minutes ago   Up 38 minutes   4369/tcp, 5671-5672/tcp, 15691-15692/tcp, 25672/tcp   inspiring_moore

If the docker container is already stopped, then in that case we need to docker startstart it first using the command as we have done here.

$ docker start dcad9f270643
dcad9f270643

Now, if the docker container is not working as expected, we can run docker container attachto see what is happening inside the container.

$ docker container attach dcad9f270643

Output:

2022-02-21 16:14:51.119742+00:00 [info] <0.466.0> Server startup complete; 3 plugins started.
2022-02-21 16:14:51.119742+00:00 [info] <0.466.0>  * rabbitmq_prometheus
2022-02-21 16:14:51.119742+00:00 [info] <0.466.0>  * rabbitmq_web_dispatch
2022-02-21 16:14:51.119742+00:00 [info] <0.466.0>  * rabbitmq_management_agent

Use Secure Shell (SSH) to enter the Docker container's shell

Finally, we can also use a secure shell, often abbreviated as SSH, to execute commands inside the container. However, this is the least recommended approach as it leads to bloat in the base image and configuration issues we may encounter.

Additionally, this approach has security issues as we need to manage the keys ourselves. We also need to consider that some images may not natively support this approach, so further configuration may be required.

However, if we need to use this method, we have to follow these steps.

• We first need to install and enable the SSH service.

• Then, we have to retrieve the container's IP address.

• Finally, we SSH into the container using the retrieved IP address.