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] [-SIG-
NAL] ] name ...
fuser -l
fuser -V
DESCRIPTION
fuser displays the PIDs of processes using the specified files or file
systems. In the default display 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 correspond-
ing name space has to be selected with the -n option. By default fuser
will look in both IPv6 and IPv4 sockets. To change the default behav-
ior, 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 op-
tion is silently ignored if -k is not present too.
-I, --inode
For the name space file let all comparisons be based on the in-
odes 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 sys-
tem 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 name-
spaces.
-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 name-
spaces.
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 ignored.
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 classified 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 prob-
lem occurs is when looking for TCP or UDP sockets when running 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 undesirable 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 device configured. There may be other de-
vices it does this for too.
The mount -m option will match any file within the same device as the
specified file, use the -M option 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 differ-
ent for stat(2) and /proc/<PID>/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)
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