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mount — mount filesystem
#include <sys/mount.h>
int
mount( |
const char *source, |
| const char *target, | |
| const char *filesystemtype, | |
| unsigned long mountflags, | |
const void *data); |
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.
Appropriate privilege (Linux: the CAP_SYS_ADMIN capability) is required to
mount 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 (e.g., "minix", "ext2",
"ext3", "jfs", "xfs", "reiserfs", "msdos", "proc", "nfs",
"iso9660"). 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
in the low order 16 bits:
MS_BIND (Linux 2.4 onward)Perform a bind mount, making a file or a directory
subtree visible at another point within a filesystem.
Bind mounts may cross filesystem boundaries and span
chroot(2) jails. The
filesystemtype
and data
arguments are ignored. Up until Linux 2.6.26,
mountflags was
also ignored (the bind mount has the same mount options
as the underlying mount point).
MS_DIRSYNC (since Linux
2.5.19)Make directory changes on this filesystem synchronous. (This property can be obtained for individual directories or subtrees using chattr(1).)
MS_MANDLOCKPermit mandatory locking on files in this filesystem. (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 filesystem.
MS_NODEVDo not allow access to devices (special files) on this filesystem.
MS_NODIRATIMEDo not update access times for directories on this
filesystem. 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 filesystem.
MS_NOSUIDDo not honor set-user-ID and set-group-ID bits when executing programs from this filesystem.
MS_RDONLYMount filesystem read-only.
MS_RELATIME (Since Linux
2.6.20)When a file on this filesystem is accessed, update
the file's last access time (atime) only if the current
value of atime is less than or equal to the file's last
modification time (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. Since Linux 2.6.30, the kernel defaults to
the behavior provided by this flag (unless MS_NOATIME was specified), and the
MS_STRICTATIME flag is
required to obtain traditional semantics. In addition,
since Linux 2.6.30, the file's last access time is
always updated if it is more than 1 day old.
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 filesystem. target should be the same
value specified in the initial mount() call; source and filesystemtype are
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 2.4.10, the following could
also be changed: MS_NOSUID, MS_NODEV, MS_NOEXEC.
MS_SILENT (since Linux
2.6.17)Suppress the display of certain (printk()) warning messages in the
kernel log. This flag supersedes the misnamed and
obsolete MS_VERBOSE flag
(available since Linux 2.4.12), which has the same
meaning.
MS_STRICTATIME (Since Linux
2.6.30)Always update the last access time (atime) when
files on this filesystem are accessed. (This was the
default behavior before Linux 2.6.30.) Specifying this
flag overrides the effect of setting the MS_NOATIME and MS_RELATIME flags.
MS_SYNCHRONOUSMake writes on this filesystem synchronous (as
though the O_SYNC flag to
open(2) was specified
for all file opens to this filesystem).
From Linux 2.4 onward, the MS_NODEV, MS_NOEXEC, and MS_NOSUID flags are settable on a
per-mount-point basis. From kernel 2.6.16 onward,
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 filesystems. Typically it is
a string of comma-separated options understood by this
filesystem. See mount(8) for details of the
options available for each filesystem type.
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.
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.
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 thread, the mount
point of another device, has open files, etc.).
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 '/'.
Too many links 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).
target, or a
prefix of source, is not a
directory.
The major number of the block device source is out of
range.
The caller does not have the required privileges.
The definitions of MS_DIRSYNC, MS_MOVE, MS_REC, MS_RELATIME, and MS_STRICTATIME were added to glibc headers
in version 2.12.
This function is Linux-specific and should not be used in programs intended to be portable.
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.
Starting with kernel 2.4.19, Linux provides per-process mount namespaces. A mount namespace is the set of filesystem mounts that are visible to a process. Mount-point namespaces can be (and usually are) shared between multiple processes, and changes to the namespace (i.e., mounts and unmounts) by one process are visible to all other processes sharing the same namespace. (The pre-2.4.19 Linux situation can be considered as one in which a single namespace was shared by every process on the system.)
A child process created by fork(2) shares its parent's mount namespace; the mount namespace is preserved across an execve(2).
A process can obtain a private mount namespace if: it
was created using the clone(2) CLONE_NEWNS flag, in which case its new
namespace is initialized to be a copy of the namespace of
the process that called clone(2); or it calls
unshare(2) with the
CLONE_NEWNS flag, which
causes the caller's mount namespace to obtain a private
copy of the namespace that it was previously sharing with
other processes, so that future mounts and unmounts by the
caller are invisible to other processes (except child
processes that the caller subsequently creates) and vice
versa.
The Linux-specific /proc/PID/mounts file exposes the list of
mount points in the mount namespace of the process with the
specified ID; see proc(5) for details.
This page is part of release 3.54 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/.
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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> %%%LICENSE_START(VERBATIM) 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. %%%LICENSE_END 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. 2008-10-06, mtk: move umount*() material into separate umount.2 page. 2008-10-06, mtk: Add discussion of namespaces. |