| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
UMOUNT(2) Linux Programmer's Manual UMOUNT(2)
umount, umount2 - unmount file system
#include <sys/mount.h>
int umount(const char *target);
int umount2(const char *target, int flags);
umount() 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 umount(), 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 systems.
On success, zero is returned. On error, -1 is returned, and errno is set
appropriately.
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 kernel source code for details.
EAGAIN A call to umount2() specifying MNT_EXPIRE successfully marked an unbusy
file system 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. Or, umount2() was called with MNT_EXPIRE
and either MNT_DETACH or MNT_FORCE.
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.
MNT_DETACH and MNT_EXPIRE are only available in glibc since version 2.11.
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) 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).
mount(2), path_resolution(7), mount(8), umount(8)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2010-06-19 UMOUNT(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface