@bikash pattnayak This answer on StackOverflow explains the reason in detail: https://stackoverflow.com/questions/43303507/what-does-fd-mean-exactly-in-dockerd-h-fd/43408869#43408869
Basically, docker daemon is launched by system service and “-H fd://” is required to notify systemd service that docker wants to use the socket.
Thanks for the details.
Welcome! In fact, I had the same question but didn’t know the reason. I understand it this time. Thank you for asking the question.