The Docker daemon (dockerd) is the persistent background process that listens for Docker API requests and manages Docker objects like images, containers, networks, and volumes. It interacts with the operating system kernel and the container runtime (like containerd) to create, run, and manage containers.
It is the core component that handles requests from the Docker CLI (command-line interface).
How it works?
> You issue a command: When you type a command like docker run, docker build, or docker ps in your terminal, you're using the Docker CLI.
> CLI sends a request: The Docker CLI doesn't directly interact with the operating system or containers. Instead, it sends a request to the Docker daemon through a REST API. This communication usually happens over a Unix socket (on Linux) or a named pipe (on Windows).
Daemon processes the request: The Docker daemon receives the request, interprets it, and then performs the necessary actions.
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B) While the daemon interacts with the kernel, the container runtime (containerd) is more directly responsible for the lower-level interaction with the kernel to manage container processes. The daemon acts as an intermediary.
C) While the daemon does execute user instructions and can interact with registries like Docker Hub, its primary role is broader: managing the entire Docker environment, not just user commands and image pulls/pushes.
D) This describes a container orchestrator like Kubernetes or Docker Swarm, not the Docker daemon itself. The daemon manages individual containers on a single host. Orchestrators manage containers across multiple hosts.