---
title: fuser — Identify processes using files or ports
date: 2026-10-20
time: 12:00
model: admin
category: programs
author_type: human
summary: Shows which processes hold a given file, directory or socket.
tags: program, Service and process management, fuser
---

Shows which processes hold a given file, directory or socket.

## Basic Information

| Command Name | fuser |
| --- | --- |
| One-line Introduction | Shows which processes hold a given file, directory or socket. |
| Provided by | psmisc package |
| Official Documentation | https://man7.org/linux/man-pages/man1/fuser.1.html |
| Supported Operating Systems | Linux |
| Installation Status | Package required (apt install psmisc) |
| Category | Linux service and process management (tags: Process and resource management (tags: process, file, port, mount)) |

## What is this command?

fuser reports the PIDs holding a file or directory open.

It is commonly used to find what blocks an unmount or which process owns a port.

## What problems does it solve?

- Find the cause when umount reports busy.
- Identify the process holding a port.
- Clean up processes locking a file.
- Check whether a mount is in use.
## Key features

### Processes using a file

Pass a path to print the PIDs that have it open.

- **When to use**: Diagnosing a failed unmount
- **What you get**: PID list with access modes
- **Limitations**: Some entries are hidden without privileges
### Port ownership

With -n and a tcp/udp spec it finds processes using a port.

- **When to use**: Resolving address-in-use errors
- **What you get**: The PID holding the port
- **Limitations**: Results depend on the network namespace
### Combined signaling

The -k option sends a signal to those processes.

- **When to use**: When releasing a lock and cleaning up at once
- **What you get**: The target processes terminated
- **Limitations**: Risk of killing unintended processes
## Installation and usage

### Check whether it is installed

```
fuser -V
```

apt install psmisc   # Debian/Ubuntu
dnf install psmisc   # Fedora/RHEL

## Real-world examples

### Who uses a file

Find processes using a mount point.

```
# Find processes using this mount point
fuser -vm /mnt/data
```

### Port owner

Find what holds 8080/tcp.

```
# Identify the process on port 8080
fuser -n tcp 8080
```

### Inspect then kill

Review targets, then signal them.

```
# Review, then terminate the holders
fuser -vm /mnt/data
fuser -km /mnt/data
```

---
Source (HTML): https://games.aidebatehub.com/programs/linux/services/fuser.html
This file is an auto-generated Markdown twin of the DevHub document.