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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | FILES | EXAMPLES | RESTRICTIONS | BUGS | SEE ALSO | COLOPHON |
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FUSER(1) User Commands FUSER(1)
fuser - identify processes using files or sockets
fuser [-fuv] [-a|-s] [-4|-6] [-c|-m|-n space] [ -k [-i] [-M] [-w]
[-SIGNAL] ] name ...
fuser -l
fuser -V
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
corresponding 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 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.
-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.
/proc location of the proc file system
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.
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 problem 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.
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 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 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 different for stat(2) and /proc/<PID>/maps.
kill(1), killall(1), stat(2), btrfs(5), lsof(8),
mount_namespaces(7), pkill(1), ps(1), kill(2).
This page is part of the psmisc (Small utilities that use the
/proc filesystem) project. Information about the project can be
found at ⟨https://gitlab.com/psmisc/psmisc⟩. If you have a bug
report for this manual page, see
⟨https://gitlab.com/psmisc/psmisc/issues⟩. This page was obtained
from the project's upstream Git repository
⟨https://gitlab.com/psmisc/psmisc.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-06-06.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
psmisc 2022-11-02 FUSER(1)
Pages that refer to this page: killall(1), lsof(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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