fuser(1) -v -n tcp 3000
identify processes using files or sockets
-v, --verbose
       Verbose mode. Processes are shown in a ps-like style. The fields PID, USER and COMMAND are similar
       to ps. ACCESS shows how the process accesses  the  file.  Verbose  mode  will  also  show  when  a
       particular file is being access as a mount point, knfs export or swap file. In this case kernel is
       shown instead of the PID.
-n SPACE, --namespace SPACE
       Select a different name space. The name spaces file (file names,  the  default),  udp  (local  UDP
       ports), and tcp (local TCP ports) are supported. For ports, either the port number or the symbolic
       name can be specified. If there is no ambiguity, the shortcut notation name/Ispace (e.g. 80/tcp  )
       can be used.
source manpages: fuser