The Geek Diary

fuser: command not found

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The fuser command is useful to determine which files are using system resources. One of the more common uses of this command is to determine which user is active in a filesystem, which prevents the system administrator from unmounting the filesystem:

[root@localhost ~]# umount /boot
umount: /boot: target is busy.
(In some cases useful info about processes that use the device is found by lsof(8) or fuser(1))
[root@localhost ~]# fuser -v /boot
          USER        PID ACCESS  COMMAND
/boot:    root        kernel      mount /boot
          student     29306       ..c.. bash

fuser output will include following symbols:

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.

The following table describes common options for the fuser command:

Option Description
-k or –kill Kill the process that is using the filesystem or resource.
-i or –interactive Prompt before killing the process (you must also use the -k option).
-v or –verbose Verbose; produce additional useful information.

If you encounter the below error while running the command fuser:

fuser: command not found

you may try installing the below package as per your choice of distribution:

Distribution Command
Debian apt-get install psmisc
Ubuntu apt-get install psmisc
Alpine apk add psmisc
Arch Linux pacman -S psmisc
Kali Linux apt-get install psmisc
CentOS yum install psmisc
Fedora dnf install psmisc
Raspbian apt-get install psmisc

fuser Command Examples

1. Find which processes are accessing a file or directory:

# fuser path/to/file_or_directory

2. Show more fields (`USER`, `PID`, `ACCESS` and `COMMAND`):

# fuser --verbose path/to/file_or_directory

3. Identify processes using a TCP socket:

# fuser --namespace tcp port

4. Kill all processes accessing a file or directory (sends the `SIGKILL` signal):

# fuser --kill path/to/file_or_directory

5. Find which processes are accessing the filesystem containing a specific file or directory:

# fuser --mount path/to/file_or_directory

6. Kill all processes with a TCP connection on a specific port:

# fuser --kill port/tcp

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