lsof

Lists open files and the corresponding processes. Note: Root privileges (or sudo) is required to list files opened by others. More information: https://manned.org/lsof.

lsof path/to/file

lsof -i :port

lsof -t path/to/file

lsof -u username

lsof -c process_or_command_name

lsof -p PID

lsof +D path/to/directory

lsof -i6TCP:port -sTCP:LISTEN -n -P