what does fd:// mean exactly in dockerd -H fd://

Question

Docker daemon documentation suggests the following hosts option for most setups:

dockerd -H fd://

I guess fd stands f

Answer 1

The -H fd:// syntax is used when running docker inside of systemd. Systemd itself will create a socket in the docker.socket unit file and listen to it, and this socket is connected to the docker daemon with the fd:// syntax in the docker.service unit file.