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Attach and Detach Mode

Updated Mar 11, 2022 ·

Overview​

In Docker, containers can be run in two main modes: attach mode and detach mode.

Attach Mode​

When a container is run in attach mode, the process runs in the foreground, meaning the console will not respond to any other inputs until the container exits. You can stop the process by pressing Ctrl-C.

  • Example: To run a simple web server that listens on port 8080:

    sudo docker run kodekloud/simple-webapp

  • Check Running Containers:

    To see the running containers, you can use:

    sudo docker ps

    Output Example:

    CONTAINER ID   IMAGE                     COMMAND           CREATED          STATUS          PORTS      NAMES
    734e84936864   kodekloud/simple-webapp   "python app.py"   30 seconds ago   Up 29 seconds   8080/tcp   relaxed_grothendieck

Detach Mode​

Running containers in detach mode allows them to run in the background. This is achieved using the -d flag. The terminal remains free for other commands while the container runs.

  • Example: To run an Ubuntu container that sleeps for 60 seconds in detach mode:

    sudo docker run -d ubuntu sleep 60

  • Attaching to a Running Container:

    If you need to interact with a container that is running in the background, you can attach to it by using the attach command along with the container ID or name:

    sudo docker ps
    sudo docker attach <container-id>
    sudo docker attach <container-name>

  • Interactive Mode:

    You can also run a container and automatically log into it by using the -it flag, which combines the -i (interactive) and -t (tty) options:

    sudo docker run -it -d --name nyancat2 06kellyjac/nyancat

This setup allows users to manage containers effectively based on their needs for interaction and control, whether they want a foreground process or prefer to run containers in the background.