How can you run a shell script on the host from a Docker container?

Running a shell script on the host from a Docker container is easy. We can do this using different ways like Docker volumes, bind mounts, and SSH. These methods help us run scripts from the container. This makes it simpler to work with tasks on the host system. This skill is important for developers and DevOps engineers. It helps us make our workflows faster and automate things in container environments.

In this article, we will look at different ways to run a shell script on the host from a Docker container. We will talk about using Docker volumes, running scripts with Docker exec, using bind mounts, passing commands from the container, and using SSH for running commands from far away. By the end of this guide, we will know how to run shell scripts well from within a Docker container.

  • How to run a shell script on the host from a Docker container
  • Using Docker volumes to run a shell script on the host
  • Executing a shell script on the host using Docker exec
  • Running a shell script on the host with Docker bind mounts
  • How to pass commands from a Docker container to the host shell script
  • Using SSH to execute a shell script on the host from a Docker container
  • Frequently Asked Questions

For more information on what Docker can do, you may want to read articles like What is Docker and Why Should You Use It? and How Does Docker Differ from Virtual Machines?.

Using Docker volumes to run a shell script on the host

To run a shell script on the host from a Docker container, we can use Docker volumes. We will mount a directory from the host into the container. This lets the container access and run scripts that are on the host system.

Steps to Use Docker Volumes

  1. Create a Script on the Host: First, we need to create a shell script on the host.

    echo -e '#!/bin/bash\n echo "Hello from the host!"' > /path/to/your/script.sh
chmod +x /path/to/your/script.sh

  2. Run the Docker Container with Volume Mounting: Now we run the Docker container and mount the directory with the script.

    docker run -v /path/to/your:/scripts --rm your-image-name

    In this command:

    • -v /path/to/your:/scripts mounts the host directory to /scripts in the container.
    • --rm will remove the container after it finishes.

  3. Execute the Script Inside the Container: When we are inside the container, we can run the shell script.

    docker run -v /path/to/your:/scripts --rm your-image-name bash -c "/scripts/script.sh"

Important Notes

  • Make sure the script is executable on the host.
  • The container needs permission to access the mounted directory.
  • Using Docker volumes helps us share files between the host and containers. It makes it easy to run scripts from the host.

For more info on managing Docker volumes, we can check this article on Docker volumes.

Executing a shell script on the host using Docker exec

To run a shell script on the host from a Docker container, we can use the docker exec command. This command helps us run commands inside a running container. With the right setup, we can run scripts on the host system.

Prerequisites

  • We must have Docker installed and running on our host machine.
  • We need to have a container that is already running.

Steps to Execute a Shell Script

  1. Make Sure the Host Script is Accessible: We should check that our shell script is on the host machine and can be executed. For example, if we have a script called script.sh, we use this command:

    chmod +x /path/to/script.sh

  2. Run the Container: We can start our container in interactive mode or check that it is running:

    docker run -d --name my_container ubuntu tail -f /dev/null

  3. Execute the Host Script: We will use the docker exec command to execute the script on the host. We need to provide the script path and make sure the container has access to the host file system.

    docker exec my_container bash -c "bash /path/to/script.sh"

Important Notes

  • Permissions: The user who runs the Docker container must have the rights to execute the script on the host.
  • Container User Context: If our container runs as a non-root user, we need to make sure that the user can run the host script.

Example

Here is a complete example:

  1. First, we create a shell script called script.sh on the host:

    echo -e "#!/bin/bash\necho 'Hello from the host!'" > /path/to/script.sh
chmod +x /path/to/script.sh

  2. Next, we run a Docker container:

    docker run -d --name my_container ubuntu tail -f /dev/null

  3. Finally, we execute the script from the container:

    docker exec my_container bash -c "bash /path/to/script.sh"

This will show:

Hello from the host!

Using docker exec is a simple way to run shell scripts on the host while we work inside a Docker container. We just need to set the correct permissions and paths. For more details on Docker commands, we can check the Docker command documentation.

Running a shell script on the host with Docker bind mounts

Docker bind mounts help us share files or folders between the host and the Docker container. This makes it easy to run a shell script on the host from the container. To do this, we can follow these steps:

  1. Create a Shell Script on the Host: First, we need to make a simple shell script on our host machine. For example, we can name it script.sh:

    #!/bin/bash
echo "This script is running on the host."

    We must make sure the script can run. We do this with:

    chmod +x script.sh

  2. Run a Docker Container with Bind Mount: Now we start a Docker container and bind mount the folder that has our script. We can use the -v option to create the bind mount:

    docker run -it --rm -v $(pwd):/scripts ubuntu

    This command will mount the current folder to /scripts in the container.

  3. Execute the Shell Script from the Container: After we get inside the container, we can run the shell script with this command:

    /scripts/script.sh

    This will run the script on the host, and we will see the output “This script is running on the host.”

This way is good for development. We can change scripts on the host and run them in the container without rebuilding the container. For more details on using volumes and mounts, we can check the article on how to bind mount host files to Docker containers.

How to pass commands from a Docker container to the host shell script

We can pass commands from a Docker container to a shell script on the host using different methods. Here are some simple and effective ways:

  1. Using Docker Volumes: We can mount a host directory into the container. Then, we write commands to a file in that directory. A shell script can run those commands later.

    docker run -v /path/on/host:/path/in/container my-container /bin/sh -c "echo 'command to run' >> /path/in/container/commands.sh"

  2. Using Docker exec: If we have a running container, we can run commands directly on it that work with the host.

    docker exec my-container sh -c "echo 'command to run' >> /path/on/host/commands.sh"

  3. Using Bind Mounts: This is like using volumes. Bind mounts let us share a host directory with the container. Any commands written to the file in the container will show up on the host.

    docker run -v /host/path:/container/path my-container sh -c "echo 'command to run' >> /container/path/commands.sh"

  4. Using SSH: If the host has SSH on and the container has an SSH client, we can run commands on the host using SSH.

    ssh user@host "bash -s" < /path/in/container/script.sh

  5. Using docker cp: This command helps us copy files from the container to the host. We can include scripts or command files.

    docker cp my-container:/path/in/container/commands.sh /path/on/host/commands.sh

These methods let us run or pass commands from a Docker container to a shell script on the host. This gives us good options for working between the container and the host system. For more information on Docker, we can check articles like What are Docker Volumes and How Do They Work or How to Bind Mount Host Files to Docker Containers.

Using SSH to execute a shell script on the host from a Docker container

To run a shell script on the host from a Docker container using SSH, we can follow these steps:

  1. Ensure SSH is Installed: First, we need to check if the SSH server is running on our host machine. We can install it using these commands:

    sudo apt-get install openssh-server
sudo systemctl start ssh
sudo systemctl enable ssh

  2. Setup SSH Keys: Next, we generate SSH keys in our Docker container and copy the public key to the host’s authorized_keys file. This way, we get password-less access.

    # Inside your Docker container
ssh-keygen -t rsa -b 4096 -C "your_email@example.com"
cat ~/.ssh/id_rsa.pub | ssh user@host "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"

  3. Run the Shell Script: After setting up the SSH keys, we can run a shell script from the host while inside the container. We use this command:

    ssh user@host 'bash /path/to/your/script.sh'

  4. Example: If our script is at /home/user/myscript.sh, the command will be:

    ssh user@host 'bash /home/user/myscript.sh'

  5. Troubleshooting: If we have problems, let’s check:

    • The SSH service must be running on the host.
    • The firewall should allow SSH connections.
    • The Docker container needs network access to the host.

This method helps us run scripts on the host from a Docker container securely, using SSH’s safe communication. For more details on Docker and its settings, we can check what is Docker and why should you use it.

Frequently Asked Questions

1. Can a Docker container execute commands on the host machine?

Yes, Docker containers can run commands on the host machine. There are different ways to do this. A common way is to use Docker volumes or bind mounts. These let us share files and folders between the container and the host. Also, we can use the docker exec command to run shell scripts on the host from inside the container. This helps us work well between the container and the host system.

2. What are Docker volumes, and how do they help in running scripts on the host?

Docker volumes are ways to keep data that we can share between the host and containers. When we mount a Docker volume to a certain path, we can store and run shell scripts from the host directly inside the container. This is useful because we do not need to copy files back and forth. It makes the execution process easier.

3. How can I use SSH to run a shell script on the host from a Docker container?

We can use SSH to connect safely to the host machine from a Docker container and run shell scripts. First, we need to install an SSH client in the container and set up SSH access on the host. Then, we can run a command like ssh user@host 'bash /path/to/script.sh'. This way, we can easily run scripts on the host. It helps us automate things and manage tasks from a distance.

4. What is the difference between Docker bind mounts and volumes for running scripts?

Docker bind mounts and volumes both let us share data between the host and containers, but they work in different ways. Bind mounts connect specific host files or folders to a container. This gives direct access to the host’s filesystem. On the other hand, volumes are managed by Docker. They are stored in a part of the host filesystem that Docker controls. For running shell scripts, bind mounts give us more freedom. We can change and access scripts from the host more easily.

5. How can I pass commands from a Docker container to the host shell script securely?

To pass commands from a Docker container to a host shell script safely, we can use Docker’s docker exec command with environment variables or command input. For example, we can do docker exec -it container_name bash -c 'command_to_execute' to run a command directly on the host. It is important to check that our commands are safe to avoid security issues.

For more information on Docker and what it can do, we can look at related topics like What is Docker and Why Should You Use It and How to Manage Docker Container Logs. These articles help us understand Docker better and learn good practices.