lsof can list all open files in osx. As directories, sockets are all also files in unix. lsof can also be used to find open ports/sockets/directories:

  • To list all open TCP sockets with port numbers:
    sudo lsof -i -P
  • To find processes open a folder or any file in that folder
    sudo lsof +D /the/foler
  • To find process open any file on a dev
    sudo lsof /dev/disk0s2
  • To print all found process id only
    sudo lsof -t <other commands>

Details can be looked up in the man page.