What is the name of the widely used Linux service manager that controls the Docker daemon, allowing actions like starting, stopping, and enabling it at system boot?

The widely used Linux service manager that controls the Docker daemon, allowing actions like starting, stopping, and enabling it at system boot, is systemd. systemd is the default init system and service manager for most modern Linux distributions. An init system is the very first process launched during system boot, responsible for bringing the system to a functional state and managing all subsequent processes. As a service manager, systemd supervises background programs, known as daemons or services, ensuring they start, run, and stop as required. The Docker daemon, which is the core background process that runs and manages Docker containers, is managed as one such service by systemd. To control the Docker daemon, systemd utilizes a configuration file called a unit file, typically named `docker.service`. This unit file specifies how to start the daemon (e.g., `ExecStart` command), how to stop it, and other operational parameters. When you use commands like `systemctl start docker`, `systemd` reads the `docker.service` unit file and executes the defined startup command to launch the Docker daemon. Similarly, `systemctl stop docker` instructs systemd to terminate the daemon based on the unit file's definition. To ensure the Docker daemon automatically starts whenever the Linux system boots, the command `systemctl enable docker` is used. This action configures systemd to include the `docker.service` in its boot sequence, allowing it to run persistently across system reboots. Conversely, `systemctl disable docker` removes this automatic startup configuration.