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UMOUNT
Section: Linux Programmer's Manual (2)
Updated: 2010-06-19
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NAME
umount, umount2 - unmount file system
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) 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.
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
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.
VERSIONS
MNT_DETACH
and
MNT_EXPIRE
are only available in glibc since version 2.11.
CONFORMING TO
These functions are Linux-specific and should not be used in
programs intended to be portable.
NOTES
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).
SEE ALSO
mount(2),
path_resolution(7),
mount(8),
umount(8)
COLOPHON
This page is part of release 3.27 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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