Fuser (Unix)


The Unix command fuser is used to show which processes are using a specified computer file, file system, or Unix socket.

Example

For example, to check process IDs and users accessing a USB drive:

$ fuser -m -u /mnt/usb1
/mnt/usb1: 1347c 1348c 1349c

The command displays the process identifiers of processes using the specified files or file
systems. In the default display mode, each PID is followed by a
letter denoting the type of access:
; c : current directory.
; e : executable being run.
; f : open file.
; F : open file for writing.
; r : root directory.
; m : mmap'ed file or shared library
Only the PIDs are written to standard output. Additional information is written to standard error. This makes it easier to process the output with computer programs.
The command can also be used to check what processes are using a network port:

$ fuser -v -n tcp 80
USER PID ACCESS COMMAND
80/tcp: root 3067 F.... httpd
apache 3096 F.... httpd
apache 3097 F.... httpd

The command returns a non-zero code if none of the files are
accessed or in case of a fatal error. If at least one access has succeeded, fuser returns zero.
The output of "fuser" may be useful in diagnosing "resource busy" messages arising when attempting to unmount filesystems.

Options

POSIX defines the following options:
psmisc adds the following options, among others:

Related commands

  • The list of all open files and the processes that have them open can be obtained through the lsof command.
  • The equivalent command on BSD operating systems is.