Socket already in use, but is not listed (mpd)?

Running $ mpd I am prompted with > socket: Failed to bind to '127.0.0.1:6600': Address already in use But if I run: $ sudo service mpd start and check its status, I get > systemd: Started Music Player Daemon. Note that in what is to come, assume that: $ sudo service mpd stop has been run. ### Questions - What is the difference between the two, why does one give an error, and the other not? - How can I track/find how the socket is being used? As mentioned, first we stop the service, if it is running? $ sudo service mpd stop I search over stackexchange, and the solutions mentioned don't find anything. $ sudo lsof -i -n -P|grep 6600 returns nothing $ sudo netstat -tulpn |grep 6600 return nothing $ sudo ss -npt|grep 6600 return nothing. But, again, $ mpd returns > socket: Failed to bind to '127.0.0.1:6600': Address already in use What do I not understand?