umount, umount2 - unmount file system
int umount(const char *target);
int umount2(const char *target, int flags);
() and umount2
() remove the attachment of the (topmost) file
system mounted on target
Appropriate privilege (Linux: the CAP_SYS_ADMIN
capability) is required
to unmount file systems.
Linux 2.1.116 added the umount2
() system call, which, like
(), unmounts a target, but allows additional flags
controlling the behavior of the operation:
- MNT_FORCE (since Linux 2.1.116)
- Force unmount even if busy. This can cause data loss. (Only
for NFS mounts.)
- MNT_DETACH (since Linux 2.4.11)
- Perform a lazy unmount: make the mount point unavailable
for new accesses, and actually perform the unmount when the mount point
ceases to be busy.
- MNT_EXPIRE (since Linux 2.6.8)
- Mark the mount point as expired. If a mount point is not
currently in use, then an initial call to umount2() with this flag
fails with the error EAGAIN, but marks the mount point as expired.
The mount point remains expired as long as it isn't accessed by any
process. A second umount2() call specifying MNT_EXPIRE
unmounts an expired mount point. 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 file
On success, zero is returned. On error, -1 is returned, and errno
The error values given below result from file-system type independent errors.
Each file system type may have its own special errors and its own special
behavior. See the Linux kernel source code for details.
- A call to umount2() specifying MNT_EXPIRE
successfully marked an unbusy file system as expired.
- target could not be unmounted because it is
- target points outside the user address space.
- target is not a mount point. Or, umount2()
was called with MNT_EXPIRE and either MNT_DETACH or
- A pathname was longer than MAXPATHLEN.
- A pathname was empty or had a nonexistent component.
- The kernel could not allocate a free page to copy filenames
or data into.
- The caller does not have the required privileges.
are only available in glibc since
These functions are Linux-specific and should not be used in programs intended
to be portable.
The original umount
() function was called as umount(device)
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).
This page is part of release 3.44 of the Linux man-pages
description of the project, and information about reporting bugs, can be found