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 Linux 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.
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 3.44 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/.