mount, umount, umount2 — mount and unmount filesystems
#include <sys/mount.h>
int
mount( |
const char * | source, |
| const char * | target, | |
| const char * | filesystemtype, | |
| unsigned long | mountflags, | |
| const void * | data); |
int
umount( |
const char * | target); |
int
umount2( |
const char * | target, |
| int | flags); |
mount() attaches the
filesystem specified by source (which is often a device
name, but can also be a directory name or a dummy) to the
directory specified by target.
umount() and umount2() remove the attachment of the
(topmost) filesystem mounted on target.
Appropriate privilege (Linux: the CAP_SYS_ADMIN capability) is required to
mount and unmount filesystems.
Since Linux 2.4 a single filesystem can be visible at multiple mount points, and multiple mounts can be stacked on the same mount point.
Values for the filesystemtype argument
supported by the kernel are listed in /proc/filesystems (like "minix", "ext2",
"msdos", "proc", "nfs", "iso9660" etc.). Further types may
become available when the appropriate modules are loaded.
The mountflags
argument may have the magic number 0xC0ED (MS_MGC_VAL) in the top 16 bits (this was
required in kernel versions prior to 2.4, but is no longer
required and ignored if specified), and various mount flags
(as defined in <linux/fs.h>
for libc4 and libc5 and in <sys/mount.h> for glibc2) in the low order 16
bits:
MS_BIND (Linux 2.4 onwards)Perform a bind mount, making a file or a directory
subtree visible at another point within a file system.
Bind mounts may cross file system boundaries and span
chroot(2) jails. The
filesystemtype,
mountflags, and
data arguments
are ignored.
MS_DIRSYNC (since Linux
2.5.19)Make directory changes on this file system synchronous. (This property can be obtained for individual directories or subtrees using chattr(1).)
MS_MANDLOCKPermit mandatory locking on files in this file system. (Mandatory locking must still be enabled on a per-file basis, as described in fcntl(2).)
MS_MOVEMove a subtree. source specifies an
existing mount point and target specifies the new
location. The move is atomic: at no point is the
subtree unmounted. The filesystemtype,
mountflags, and
data arguments
are ignored.
MS_NOATIMEDo not update access times for (all types of) files on this file system.
MS_NODEVDo not allow access to devices (special files) on this file system.
MS_NODIRATIMEDo not update access times for directories on this
file system. This flag provides a subset of the
functionality provided by MS_NOATIME; that is, MS_NOATIME implies MS_NODIRATIME.
MS_NOEXECDo not allow programs to be executed from this file system.
MS_NOSUIDDo not honor set-user-ID and set-group-ID bits when executing programs from this file system.
MS_RDONLYMount file system read-only.
MS_RELATIME (Since Linux
2.6.20)When a file on this file system is accessed, only update the file's last accessed time (atime) if the current value of atime is less than or equal to the file's last modified (mtime) or last status change time (ctime). This option is useful for programs, such as mutt(1), that need to know when a file has been read since it was last modified.
MS_REMOUNTRemount an existing mount. This allows you to change
the mountflags
and data of an
existing mount without having to unmount and remount
the file system. source and target should be the same
values specified in the initial mount() call; filesystemtype is
ignored.
The following mountflags can be
changed: MS_RDONLY,
MS_SYNCHRONOUS,
MS_MANDLOCK; before
kernel 2.6.16, the following could also be changed:
MS_NOATIME and
MS_NODIRATIME; and,
additionally, before kernel 2.4, the following could
also be changed: MS_NOSUID, MS_NODEV, MS_NOEXEC.
MS_SYNCHRONOUSMake writes on this file system synchronous (as
though the O_SYNC flag to
open(2) was specified
for all file opens to this file system).
From Linux 2.4 onwards, the MS_NODEV, MS_NOEXEC, and MS_NOSUID flags are settable on a
per-mount-point basis. From kernel 2.6.16 onwards,
MS_NOATIME and MS_NODIRATIME are also settable on a
per-mount-point basis. The MS_RELATIME flag is also settable on a
per-mount-point basis.
The data argument
is interpreted by the different file systems. Typically it is
a string of comma-separated options understood by this file
system. See mount(8) for details of the
options available for each filesystem type.
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.
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 kernel source code for details.
A component of a path was not searchable. (See also
path_resolution(7).)
Or, mounting a read-only filesystem was attempted
without giving the MS_RDONLY flag. Or, the block device
source is
located on a filesystem mounted with the MS_NODEV option.
A call to umount2()
specifying MNT_EXPIRE
successfully marked an unbusy file system as
expired.
source is
already mounted. Or, it cannot be remounted read-only,
because it still holds files open for writing. Or, it
cannot be mounted on target because target is still busy (it
is the working directory of some task, the mount point
of another device, has open files, etc.). Or, it could
not be unmounted because it is busy.
One of the pointer arguments points outside the user address space.
source had
an invalid superblock. Or, a remount (MS_REMOUNT) was attempted, but
source was not
already mounted on target. Or, a move
(MS_MOVE) was attempted,
but source was
not a mount point, or was '/'. Or, an unmount was
attempted, but target was not a mount
point. Or, umount2() was
called with MNT_EXPIRE
and either MNT_DETACH or
MNT_FORCE.
Too many link encountered during pathname
resolution. Or, a move was attempted, while target is a descendant of
source.
(In case no block device is required:) Table of dummy devices is full.
A pathname was longer than MAXPATHLEN.
filesystemtype not
configured in the kernel.
A pathname was empty or had a nonexistent component.
The kernel could not allocate a free page to copy filenames or data into.
source is
not a block device (and a device was required).
The second argument, or a prefix of the first argument, is not a directory.
The major number of the block device source is out of
range.
The caller does not have the required privileges.
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).
The original MS_SYNC flag
was renamed MS_SYNCHRONOUS in
1.1.69 when a different MS_SYNC was added to <mman.h>
Before Linux 2.4 an attempt to execute a set-user-ID or
set-group-ID program on a filesystem mounted with
MS_NOSUID would fail with
EPERM. Since Linux 2.4 the
set-user-ID and set-group-ID bits are just silently ignored
in this case.
This page is part of release 2.79 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/.
|
Copyright (C) 1993 Rickard E. Faith <faithcs.unc.edu> and Copyright (C) 1994 Andries E. Brouwer <aebcwi.nl> and Copyright (C) 2002, 2005 Michael Kerrisk <mtk.manpagesgmail.com> Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. Modified 1996-11-04 by Eric S. Raymond <esrthyrsus.com> Modified 2001-10-13 by Michael Kerrisk <mtk.manpagesgmail.com> Added note on historical behavior of MS_NOSUID Modified 2002-05-16 by Michael Kerrisk <mtk.manpagesgmail.com> Extensive changes and additions Modified 2002-05-27 by aeb Modified 2002-06-11 by Michael Kerrisk <mtk.manpagesgmail.com> Enhanced descriptions of MS_MOVE, MS_BIND, and MS_REMOUNT Modified 2004-06-17 by Michael Kerrisk <mtk.manpagesgmail.com> 2005-05-18, mtk, Added MNT_EXPIRE, plus a few other tidy-ups. |