💡 Performance & Debugging September 24, 2026 9

Linux Command: fuser

Identify processes using files or sockets

Terminal — Performance & Debugging

Command

$ fuser -vm /mnt/usb/

Output

USER PID ACCESS COMMAND user 1234 ..c.. bash user 5678 ...e. vim

fuser identifies processes using files, directories, or sockets. It shows which processes have a resource open, and can optionally kill them. It is simpler than lsof for specific use cases. fuser is most commonly used to find processes preventing a filesystem from being unmounted, or to identify which process is listening on a specific port. fuser can send signals to the identified processes, making it a one-command solution for "find and kill" scenarios.

Syntax

fuser [OPTION]... NAME...

Key Options

-v — Verbose output
-m — Show processes using mounted filesystem
-k — Kill processes using the resource
-n tcp — Show process using TCP port
-i — Interactive (ask before killing)

Examples

Find processes on mount

fuser -vm /mnt/usb/

Output: USER PID ACCESS COMMAND user 1234 ..c.. bash user 5678 ...e. vim

Kill processes on mount

sudo fuser -km /mnt/usb/

Check port usage

fuser -vn tcp 80

Output: 80/tcp: 1234

Pro Tips

Cannot unmount? fuser -km /mount/point kills blocking processes. Then umount succeeds.
fuser is simpler for "who uses this file/port?" lsof is more detailed for comprehensive diagnostics.
fuser -k sends SIGKILL by default. Use -ki for interactive mode to confirm each kill.

Learn more: Full fuser reference →