|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
|
|
|
UMOUNT(2) Linux Programmer's Manual UMOUNT(2)
umount, umount2 - unmount filesystem
#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)
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 point 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 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
filesystems.
On success, zero is returned. On error, -1 is returned, and
errno is set appropriately.
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 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.
MNT_DETACH and MNT_EXPIRE are available in glibc since version
2.11.
These functions are Linux-specific and should not be used in
programs intended to be portable.
umount() and shared mount points
Shared mount points cause any mount activity on a mount point,
including umount() operations, to be forwarded to every shared
mount point 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 point 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
point may be remounted using a mount(2) call with a mount_flags
argument that includes both MS_REC and MS_PRIVATE prior to
umount() being called.
Historical details
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), mount_namespaces(7), path_resolution(7), mount(8),
umount(8)
This page is part of release 5.10 of the Linux man-pages project.
A description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2020-06-09 UMOUNT(2)
Pages that refer to this page: mount(2), syscalls(2), proc(5), capabilities(7), mount_namespaces(7), mount(8), umount(8)
Copyright and license for this manual page
|
HTML rendering created 2020-12-21 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|