---
title: umount — Unmount a filesystem
date: 2026-10-20
time: 12:00
model: admin
category: programs
author_type: human
summary: Detaches a mounted filesystem so a device can be removed without losing data.
tags: program, File and disk management, umount
---

Detaches a mounted filesystem so a device can be removed without losing data.

## Basic Information

| Command Name | umount |
| --- | --- |
| One-line Introduction | Detaches a mounted filesystem so a device can be removed without losing data. |
| Provided by | util-linux (included in every Linux distribution) |
| Official Documentation | https://man7.org/linux/man-pages/man8/umount.8.html |
| Supported Operating Systems | Linux, macOS, BSD |
| Installation Status | Installed by default (no separate installation needed) |
| Category | Linux file and disk management (tags: mount, filesystem, disk, detach) |

## What is this command?

umount removes a mount point from the kernel's mount table. It flushes pending writes to the device, so it must be run before unplugging a USB stick or external disk.

It accepts either the device name (/dev/sdb1) or the mount point (/mnt/usb).

## What problems does it solve?

- Safely detaching an external disk.
- Unmounting before running a filesystem check.
- Disconnecting an NFS or network share that is no longer needed.
- Remounting with different options.
## Key features

### Device or mount point

You can pass either the device path or the directory path.

- **When to use**: Scripts that only know the device name
- **What you get**: No need to look up the mount point
- **Limitations**: If a device is mounted twice, only one mount is removed
### Detecting busy mounts

A busy error means the mount is in use; lsof or fuser finds the process.

- **When to use**: When you see a device is busy error
- **What you get**: Shows which process holds the mount
- **Limitations**: Forcing the unmount risks data loss
### Lazy unmount

The lazy option detaches immediately and cleans up remaining references later.

- **When to use**: Disconnecting an unresponsive network mount
- **What you get**: The shell does not hang
- **Limitations**: Resources may linger until cleanup completes
## Installation and usage

### Check whether it is installed

```
which umount
umount --version
```

It is part of util-linux, so no separate installation is needed.

## Real-world examples

### Unmount by mount point

The most common form.

```
# Unmount /mnt/usb
sudo umount /mnt/usb
```

### Find the process holding it

When unmount is refused, check which process is accessing it.

```
# Find the cause of busy
sudo lsof /mnt/usb
sudo fuser -vm /mnt/usb
```

### Lazy unmount

Used for unresponsive remote mounts.

```
# Detach now, clean up later
sudo umount -l /mnt/nfs
```

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