Manual: fuser

FUSER(1)					User Commands					    FUSER(1)

NAME
       fuser - identify processes using files or sockets

SYNOPSIS
       fuser [-fuv] [-a|-s] [-4|-6] [-c|-m|-n space] [ -k [-i] [-M] [-w] [-SIGNAL] ] name ...
       fuser -l
       fuser -V

DESCRIPTION
       fuser  displays the PIDs of processes using the specified files or file systems.	 In the default dis‐
       play mode, each file name is followed by a letter denoting the type of access:

	      c	     current directory.
	      e	     executable being run.
	      f	     open file.	 f is omitted in default display mode.
	      F	     open file for writing.  F is omitted in default display mode.
	      r	     root directory.
	      m	     mmap'ed file or shared library.
	      .	     Placeholder, omitted in default display mode.

       fuser returns a non-zero return code if none of the specified files is accessed or in case of a fatal
       error.  If at least one access has been found, fuser returns zero.

       In order to look up processes using TCP and UDP sockets, the corresponding name space has to  be	 se‐
       lected  with  the -n option. By default fuser will look in both IPv6 and IPv4 sockets.  To change the
       default behavior, use the -4 and -6 options.  The socket(s) can be specified by the local and  remote
       port, and the remote address.  All fields are optional, but commas in front of missing fields must be
       present:

       [lcl_port][,[rmt_host][,[rmt_port]]]

       Either symbolic or numeric values can be used for IP addresses and port numbers.

       fuser outputs only the PIDs to stdout, everything else is sent to stderr.

OPTIONS
       -a, --all
	      Show  all files specified on the command line.  By default, only files that are accessed by at
	      least one process are shown.

       -c     Same as -m option, used for POSIX compatibility.

       -f     Silently ignored, used for POSIX compatibility.

       -k, --kill
	      Kill processes accessing the file.  Unless changed with -SIGNAL, SIGKILL is  sent.   An  fuser
	      process  never kills itself, but may kill other fuser processes.	The effective user ID of the
	      process executing fuser is set to its real user ID before attempting to kill.

       -i, --interactive
	      Ask the user for confirmation before killing a process.  This option is silently ignored if -k
	      is not present too.

       -I, --inode
	      For the name space file let all comparisons be based on the inodes of  the  specified  file(s)
	      and never on the file names even on network based file systems.

       -l, --list-signals
	      List all known signal names.

       -m NAME, --mount NAME
	      NAME  specifies  a  file	on  a  mounted	file  system or a block device that is mounted.	 All
	      processes accessing files on that file system are listed.	 If a directory is specified, it  is
	      automatically changed to NAME/ to use any file system that might be mounted on that directory.

       -M, --ismountpoint
	      Request  will  be	 fulfilled  only if NAME specifies a mountpoint.  This is an invaluable seat
	      belt which prevents you from killing the machine if NAME happens to not be a filesystem.

       -w     Kill only processes which have write access.  This option is silently ignored  if	 -k  is	 not
	      present too.

       -n NAMESPACE, --namespace NAMESPACE
	      Select a different name space.  The name spaces file (file names, the default), udp (local UDP
	      ports),  and  tcp	 (local	 TCP ports) are supported.  For ports, either the port number or the
	      symbolic name can be specified.  If there is no ambiguity, the  shortcut	notation  name/space
	      (e.g., 80/tcp) can be used.

       -s, --silent
	      Silent operation.	 -u and -v are ignored in this mode.  -a must not be used with -s.

       -SIGNAL
	      Use  the specified signal instead of SIGKILL when killing processes.  Signals can be specified
	      either by name (e.g., -HUP) or by number (e.g., -1).  This option is silently ignored  if	 the
	      -k option is not used.

       -u, --user
	      Append the user name of the process owner to each PID.

       -v, --verbose
	      Verbose  mode.   Processes are shown in a ps-like style.	The fields PID, USER and COMMAND are
	      similar to ps.  ACCESS shows how the process accesses the file.  Verbose mode will  also	show
	      when  a particular file is being accessed as a mount point, knfs export or swap file.  In this
	      case kernel is shown instead of the PID.

       -V, --version
	      Display version information.

       -4, --ipv4
	      Search only for IPv4 sockets.  This option must not be used with the -6 option and only has an
	      effect with the tcp and udp namespaces.

       -6, --ipv6
	      Search only for IPv6 sockets.  This option must not be used with the -4 option and only has an
	      effect with the tcp and udp namespaces.

FILES
       /proc  location of the proc file system

EXAMPLES
       fuser -km /home
	      kills all processes accessing the file system /home in any way.

       if fuser -s /dev/ttyS1; then :; else command; fi
	      invokes command if no other process is using /dev/ttyS1.

       fuser telnet/tcp
	      shows all processes at the (local) TELNET port.

RESTRICTIONS
       Processes accessing the same file or file system several times in the same way are only shown once.

       If the same object is specified several times on the command line, some of those entries may  be	 ig‐
       nored.

       fuser  may  only be able to gather partial information unless run with privileges.  As a consequence,
       files opened by processes belonging to other users may not be listed and executables may	 be  classi‐
       fied as mapped only.

       fuser  cannot  report on any processes that it doesn't have permission to look at the file descriptor
       table for.  The most common time this problem occurs is when looking for TCP or UDP sockets when run‐
       ning fuser as a non-root user.  In this case fuser will report no access.

       Installing fuser SUID root will avoid problems associated with partial information, but may be  unde‐
       sirable for security and privacy reasons.

       udp and tcp name spaces, and UNIX domain sockets can't be searched with kernels older than 1.3.78.

       Accesses by the kernel are only shown with the -v option.

       The  -k	option	only works on processes.  If the user is the kernel, fuser will print an advice, but
       take no action beyond that.

       fuser will not see block devices mounted by processes in a different mount namespace.  This is due to
       the device ID shown in the process' file descriptor table  being	 from  the  process  namespace,	 not
       fuser's; meaning it won't match.

BUGS
       fuser -m /dev/sgX will show (or kill with the -k flag) all processes, even if you don't have that de‐
       vice configured.	 There may be other devices it does this for too.

       The  mount -m option will match any file within the same device as the specified file, use the -M op‐
       tion as well if you mean to specify only the mount point.

       fuser will not match mapped files, such as a process' shared libraries if  they	are  on	 a  btrfs(5)
       filesystem due to the device IDs being different for stat(2) and /proc//maps.

SEE ALSO
       kill(1), killall(1), stat(2), btrfs(5), lsof(8), mount_namespaces(7), pkill(1), ps(1), kill(2).

psmisc						 2022-11-02					    FUSER(1)