ss: socket stats summary

More lsof commands

• ss: filter by destination port
  ss -tnp dst :443copy

  Show connections going TO port 443

• Find owner of port
  lsof -nP -i :<port>copy

  Show which process owns a port; -nP skips DNS/service name lookups for speed

• All listening sockets
  lsof -nP -iTCP -sTCP:LISTENcopy

  List every TCP listener with PID, no name resolution; modern: ss -ltnp

• Deleted open files
  lsof +L1copy

  Find unlinked files still held open eating disk; df shows full but du does not

• Who holds a file before umount
  lsof /mnt/<name>copy

  Reveal processes blocking a 'device busy' umount; pass the mountpoint path

all 19 lsof commands →