fuser - macOS


The fuser command in macOS identifies the processes using files or sockets. Primarily, it’s used for system management tasks, to ensure resources are correctly allocated, and to solve issues related to file locking by determining which processes are using a specified file, directories, or sockets. It is particularly effective in troubleshooting system issues and managing server environments.


fuser [options] file_or_directory [file_or_directory ...]


  • file_or_directory: Specify the file, directory, or socket to check for process usage.


  • -c: Target the given mount point.
  • -k: Kill processes accessing the file. Optionally, it accepts signal names (e.g., -k SIGKILL).
  • -u: Append the user ID of the process owner to the output.
  • -v: Verbose mode; increases the amount of information displayed.
  • -n space: Define the namespace (file, udp, or tcp).

Typical Use Cases:

  • -c is used when you want to see all processes accessing a particular mount point.
  • -k is very useful for freeing up files that are locked by processes.
  • -u is helpful for administrators to see which user owns the process engaging the file.


  1. Check which processes are using a specific file:

    fuser -u /path/to/file.txt

    This command will list processes using file.txt along with the user IDs.

  2. Kill all processes using a specific directory:

    fuser -k /path/to/directory/

    This command sends a SIGTERM to all processes using files inside the specified directory.

  3. Verbose output for a specific network port using TCP:

    fuser -v -n tcp 8080

    This displays more detailed information about the processes using TCP port 8080.

Common Issues

  • Permission Denied: Without sufficient permissions, fuser will not show all processes. Running it with sudo may be necessary.
  • Process not found: If fuser returns no output, it could mean no processes are currently accessing the file, or the path specified is incorrect.


Use fuser in combination with other commands for powerful system management scripts. For instance, to force unmount a drive that says it’s in use:

fuser -k /mnt/drive
umount /mnt/drive

This kills processes that are using the mount point /mnt/drive, then unmounts it.

  • lsof: Similar to fuser, it lists open files and the processes that opened them.
  • ps: Used to display information about running processes.

For further reading and more detailed information about the fuser command, consult the manual pages (available via man fuser in the terminal) or visit the online macOS documentation.