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.

• Find the processes that have a given file open:
  lsof {{path/to/file}}
• Find the process that opened a local internet port:
  lsof -i :{{port}}
• Only output the process ID (PID):
  lsof -t {{path/to/file}}
• List files opened by the given user:
  lsof -u {{username}}
• List files opened by the given command or process:
  lsof -c {{process_or_command_name}}
• List files opened by a specific process, given its PID:
  lsof -p {{PID}}
• List open files in a directory:
  lsof +D {{path/to/directory}}
• Find the process that is listening on a local IPv6 TCP port and don't convert network or port numbers:
  lsof -i6TCP:{{port}} -sTCP:LISTEN -n -P