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Docker containers are a standard unit for packaging all the dependencies of an application, allowing us to easily run them in any environment. Containers have become very popular recently, and most developers now rely heavily on containers to manage their applications and dependencies.

Docker provides us with multiple ways to access a shell instance by launching a bash terminal in a docker container. This is particularly useful when running certain commands inside a docker container.

Additionally, this could also be for debugging reasons or you might want to check if everything is configured correctly. This article explores the different methods we can use to run containers and not run containers.

Using the Bash Interactive Shell

Bash is a common command processor in Linux systems that allows users to enter commands that result in actions. If you have interacted with Unix-based systems or WSL at all, you have probably interacted with various commands through bash.

Similarly, we can also directly access the Linux terminal in the docker container and execute commands just like using a normal Linux bash. One advantage of this approach is that we can do this with a non-running container, docker execunlike other commands such as the command.

As shown below, we will use the official image from the docker registry rabbitmqto create a docker container and directly access bash inside the container. You can do this with any other command; just make sure you have the image beforehand.

docker pull rabbitmq
docker images

Now that we have the image, we can create the docker container interactively. This means we can run commands inside the docker container while it is running as shown below.

$ docker run -it rabbitmq bash

Output:

root@f418a3286aae:/#

As you can see, we are now inside the docker container and we have successfully run bash inside the new container. We can now execute commands as if we were using a real terminal.

For example, we can list the files and directories inside this container as follows.

root@f418a3286aae:/# ls
bin  boot  dev  etc  home  lib  lib32  lib64  libx32  media  mnt  opt  plugins  proc  root  run  sbin  srv  sys  tmp  usr  var
root@f418a3286aae:/#

Use docker execthe command

Alternatively, we can also docker execrun bash in a new docker container using the command. However, unlike the previous method, this command requires that we already have the container running; otherwise, the command will not work.

Use docker ps -athe command to confirm that our container is running. If the container you want to use is not running, you may need to docker startstart it using the command followed by the container ID or name.

docker ps

We will -ituse docker execthe command alongside the docker tag. execThe docker command allows us to execute commands within a running container, while -itthe docker tag allows us to open a container interactively.

We can execute as shown below.

$ docker exec -it f418a3286aae bash

Output:

root@f418a3286aae:/# ls
bin  boot  dev  etc  home  isaac  lib  lib32  lib64  libx32  media  mnt  opt  plugins  proc  root  run  sbin  srv  sys tmp  tonyloi  usr  var

Now that we have successfully started bash in this docker container, we can run various commands in the container. We can also use it for containers without bash sh.

This is also a command that will open up a basic shell prompt where we can run our commands within the container.

$ docker exec -it f418a3286aae sh

Output:

# ls
bin  boot  dev  etc  home  isaac  isaactonyloi  lib  lib32  lib64  libx32  media  mnt  opt  plugins  proc  root  run  sbin  srv  sys  tmp  tonyloi  usr  var

Use docker attachthe command

We can also docker attachstart bash inside a running docker container using the command. This allows us to attach the local standard input, output, and error streams to the running container using the container's ID.

We can then run various commands, accept input, and debug a specific container. We need a running container to attach our output, input, and error streams to.

We can achieve this using either the container name or the id as shown below.

Code:

$ docker container attach f418a3286aae

Output:

root@f418a3286aae:/# ls
bin  boot  dev  etc  home  isaac  isaactonyloi  lib  lib32  lib64  libx32  media  mnt  opt  plugins  proc  root  run  sbin  srv  sys  tmp  tonyloi  usr  var
root@f418a3286aae:/#