For at least _some_ *BSDs (Net, Free. Don't know about Open, Dragon Fly), see fstat(1) and sockstat(1) for functionally similar tools that ship with the base sy

For at least _some_ *BSDs (Net, Free. Don't know about Open, Dragon Fly), see fstat(1) and sockstat(1) for functionally similar tools that ship with the base system. lsof(1) isn't part of base, but is available via ports/pkgsrc if lsof(1) is required or desired.