实操了docker也要几天，那么问题来了，啥是dockerd？？？？？？结尾加个d，--help之后就完全不一样了：
dockerd is the persistent process that manages containers. Docker uses different binaries for the daemon and client. To run the daemon you type dockerd
The daemon is:
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a self-sufficient runtime for containers.
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a background service running on the host that manages building, running and distributing Docker containers.
The daemon creates and manages Docker objects, such as:
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and volumes.
The Docker daemon (dockerd) listens for Docker API requests. A daemon can also communicate with other daemons to manage Docker services.