fuser - Linux

Overview

The fuser command in Linux is a powerful tool used for identifying process IDs using files or sockets. It is conducive in system administration, providing insights into process-resource relationships and enabling the resolution of resource conflicts by pinpointing which processes are using specified files or mounted filesystems.

Syntax

The basic syntax of the fuser command is as follows:

fuser [options] filename(s)/mountpoint(s)

Options/Flags

  • -a, –all: Display all specified files, whether accessed or not.
  • -k, –kill: Kills processes accessing the file. By default, a SIGKILL signal is sent.
  • -i, –interactive: Used with -k, asks for confirmation before killing a process.
  • -m, –mount: Identifies processes using files within a mounted filesystem.
  • -u, –user: Shows the user name of the process owner after the PID.
  • -v, –verbose: Provides detailed output, including user, PID, access, and command.
  • -n SPACE: Specifies the namespace (file, udp, or tcp) to search for processes.
  • -s SIGNAL, –signal SIGNAL: Instead of SIGKILL, send a specified signal.

Examples

  1. Identifying processes using a specific file: 
    fuser /home/user/example.txt
  2. Killing all processes accessing a specific mount point: 
    fuser -km /mnt/data
  3. Displaying verbose information about the processes using TCP sockets: 
    fuser -v -n tcp 80

Common Issues

  • Permission Errors: Running fuser without sufficient permissions results in no output. Use sudo to run fuser with administrative privileges.
  • Resource not found: Ensure the correct path or resource name is used, particularly for mount points or network resources.

Integration

fuser can be combined with other commands for advanced monitoring and scripting. Below is an example that uses fuser with grep to filter processes based on specific criteria:

fuser /var/www/html/index.php 2>&1 | grep 'httpd'

This command checks who is using index.php and filters for ‘httpd’ related processes.

  • lsof: Lists open files and the processes that opened them.
  • kill: Send signals to processes, typically to terminate the process.

Further Reading: Visit the Linux manual page online: fuser Man Page

This manual provides a clear understanding of usage, options, and examples for incorporating fuser in system management tasks effectively.