Linux fuser command
On Unix-like operating systems, the fuser command identifies processes that are currently using files or sockets on the system.
This page describes the GNU/Linux version of fuser.
Description
fuser displays the PIDs (Process IDentifier) 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. |
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 is found, fuser returns zero.
To look up processes using TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) sockets, the corresponding name space has to be selected with the -n option. By default, fuser looks 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.
Syntax
fuser [-fuv] [-a|-s] [-4|-6] [-c|-m|-n space] [ -k [-i] [-M] [-w]
[-SIGNAL] ] name ...
fuser -l
fuser -V
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 also present. |
| -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 file is specified, it is automatically changed to NAME/. to use any file system that might be mounted on that directory. |
| -M, --ismountpoint | Request is fulfilled only if NAME specifies a mountpoint. This is an invaluable seatbelt 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 also present. |
| -n SPACE, --namespace SPACE |
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 also present. |
| -u, --user | Append the username 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 also shows when a particular file is being access 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. |
| - | Reset all options and set the signal back to SIGKILL. |
Examples
fuser .
Display every process ID that uses the current directory ("./").
fuser -v .
Display verbose information about every process that uses the current directory. This information includes the name of the user who initiated the process and an indicator of the process name.
fuser -v /
Display verbose information about every process that uses the root directory.
Related commands
kill — Send a signal to a process, affecting its behavior or killing it.
pkill — Send a signal to any process whose attributes match a regular expression.
ps — Report the status of a process or processes.