$ Linux Command

Processes

lsof

List open files and the processes using them.

filesprocessportstroubleshoot

Additional Notes

lsof is a process-management command used to list open files and the processes using them. It is an essential troubleshooting tool for identifying which process holds a file, port, or device open.

lsof requires read access to /dev/fd and /proc on Linux. Some information may be restricted to the file owner or require root privileges to view.

Syntax

lsof [options] [file ...]

Parameters

  • options: Flags that change how lsof behaves.
  • file: Optional file, directory, device, or socket target.

Common Options

  • -i: Show network files.
  • -i :PORT: Show processes using a port.
  • +D DIR: Show open files under a directory.
  • -u USER: Show files opened by a user.

Examples

lsof -i :8080
lsof +D /mnt/usb
lsof -u www-data

Practical Notes

lsof helps explain why a port is busy or why a filesystem cannot be unmounted.