---
name: "umount2"
section: "2"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/umount/2"
---

# umount2(2)

unmount filesystem

Part of [umount(2)](/umount/2.md).

## NAME

umount, umount2 - unmount filesystem

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <sys/mount.h>
```

**int umount(const char \****target***);** **int umount2(const char \****target***, int** *flags***);**

## DESCRIPTION

**umount**() and **umount2**() remove the attachment of the (topmost) filesystem mounted on *target*.

Appropriate privilege (Linux: the **CAP\_SYS\_ADMIN** capability) is required to unmount filesystems.

Linux 2.1.116 added the **umount2**() system call, which, like **umount**(), unmounts a target, but allows additional *flags* controlling the behavior of the operation:

- **MNT\_FORCE** (since Linux 2.1.116)

  Ask the filesystem to abort pending requests before attempting the unmount. This may allow the unmount to complete without waiting for an inaccessible server, but could cause data loss. If, after aborting requests, some processes still have active references to the filesystem, the unmount will still fail. As at Linux 4.12, **MNT\_FORCE** is supported only on the following filesystems: 9p (since Linux 2.6.16), ceph (since Linux 2.6.34), cifs (since Linux 2.6.12), fuse (since Linux 2.6.16), lustre (since Linux 3.11), and NFS (since Linux 2.1.116).

- **MNT\_DETACH** (since Linux 2.4.11)

  Perform a lazy unmount: make the mount unavailable for new accesses, immediately disconnect the filesystem and all filesystems mounted below it from each other and from the mount table, and actually perform the unmount when the mount ceases to be busy.

- **MNT\_EXPIRE** (since Linux 2.6.8)

  Mark the mount as expired. If a mount is not currently in use, then an initial call to **umount2**() with this flag fails with the error **EAGAIN**, but marks the mount as expired. The mount remains expired as long as it isn't accessed by any process. A second **umount2**() call specifying **MNT\_EXPIRE** unmounts an expired mount. This flag cannot be specified with either **MNT\_FORCE** or **MNT\_DETACH**.

- **UMOUNT\_NOFOLLOW** (since Linux 2.6.34)

  Don't dereference *target* if it is a symbolic link. This flag allows security problems to be avoided in set-user-ID-*root* programs that allow unprivileged users to unmount filesystems.

## RETURN VALUE

On success, zero is returned. On error, -1 is returned, and *errno* is set to indicate the error.

## ERRORS

The error values given below result from filesystem type independent errors. Each filesystem type may have its own special errors and its own special behavior. See the Linux kernel source code for details.

- **EAGAIN**

  A call to **umount2**() specifying **MNT\_EXPIRE** successfully marked an unbusy filesystem as expired.

- **EBUSY**

  *target* could not be unmounted because it is busy.

- **EFAULT**

  *target* points outside the user address space.

- **EINVAL**

  *target* is not a mount point.

- **EINVAL**

  *target* is locked; see [**mount\_namespaces**(7)](/mount_namespaces/7.md).

- **EINVAL**

  **umount2**() was called with **MNT\_EXPIRE** and either **MNT\_DETACH** or **MNT\_FORCE**.

- **EINVAL** (since Linux 2.6.34)

  **umount2**() was called with an invalid flag value in *flags*.

- **ENAMETOOLONG**

  A pathname was longer than **MAXPATHLEN**.

- **ENOENT**

  A pathname was empty or had a nonexistent component.

- **ENOMEM**

  The kernel could not allocate a free page to copy filenames or data into.

- **EPERM**

  The caller does not have the required privileges.

## STANDARDS

Linux.

## HISTORY

**MNT\_DETACH** and **MNT\_EXPIRE** are available since glibc 2.11.

The original **umount**() function was called as *umount(device)* and would return **ENOTBLK** when called with something other than a block device. In Linux 0.98p4, a call *umount(dir)* was added, in order to support anonymous devices. In Linux 2.3.99-pre7, the call *umount(device)* was removed, leaving only *umount(dir)* (since now devices can be mounted in more than one place, so specifying the device does not suffice).

## NOTES

### umount() and shared mounts

Shared mounts cause any mount activity on a mount, including **umount**() operations, to be forwarded to every shared mount in the peer group and every slave mount of that peer group. This means that **umount**() of any peer in a set of shared mounts will cause all of its peers to be unmounted and all of their slaves to be unmounted as well.

This propagation of unmount activity can be particularly surprising on systems where every mount is shared by default. On such systems, recursively bind mounting the root directory of the filesystem onto a subdirectory and then later unmounting that subdirectory with **MNT\_DETACH** will cause every mount in the mount namespace to be lazily unmounted.

To ensure **umount**() does not propagate in this fashion, the mount may be remounted using a [**mount**(2)](/mount/2.md) call with a *mount\_flags* argument that includes both **MS\_REC** and **MS\_PRIVATE** prior to **umount**() being called.

## SEE ALSO

[**mount**(2)](/mount/2.md), [**mount\_namespaces**(7)](/mount_namespaces/7.md), [**path\_resolution**(7)](/path_resolution/7.md), [**mount**(8)](/mount/8.md), [**umount**(8)](/umount/8.md)