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MOUNT(2) Linux Programmer's Manual MOUNT(2)
mount - mount file system
#include <sys/mount.h>
int mount(const char *source, const char *target,
const char *filesystemtype, unsigned long mountflags,
const void *data);
mount() attaches the file system 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 file systems.
Since Linux 2.4 a single file system 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", "ext3", "jfs", "xfs", "reiserfs",
"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 onward)
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 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). Since Linux 2.6.26, the MS_RDONLY flag is honored when
making a bind mount.
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_MANDLOCK
Permit 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_MOVE
Move 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_NOATIME
Do not update access times for (all types of) files on this file
system.
MS_NODEV
Do not allow access to devices (special files) on this file system.
MS_NODIRATIME
Do 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_NOEXEC
Do not allow programs to be executed from this file system.
MS_NOSUID
Do not honor set-user-ID and set-group-ID bits when executing programs
from this file system.
MS_RDONLY
Mount 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 access time (atime) 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_REMOUNT
Remount 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 2.4.10,
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 file
system 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_SYNCHRONOUS
Make 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 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 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.
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 file-system type may have its own special errors and its own special
behavior. See the kernel source code for details.
EACCES A component of a path was not searchable. (See also
path_resolution(7).) Or, mounting a read-only file system was
attempted without giving the MS_RDONLY flag. Or, the block device
source is located on a file system mounted with the MS_NODEV option.
EBUSY 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.).
EFAULT One of the pointer arguments points outside the user address space.
EINVAL 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 '/'.
ELOOP Too many links encountered during pathname resolution. Or, a move was
attempted, while target is a descendant of source.
EMFILE (In case no block device is required:) Table of dummy devices is full.
ENAMETOOLONG
A pathname was longer than MAXPATHLEN.
ENODEV filesystemtype not configured in the kernel.
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.
ENOTBLK
source is not a block device (and a device was required).
ENOTDIR
target, or a prefix of source, is not a directory.
ENXIO The major number of the block device source is out of range.
EPERM The caller does not have the required privileges.
The definitions of MS_DIRSYNC, MS_MOVE, MS_REC, MS_RELATIME, and
MS_STRICTATIME were only 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 file system 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 file system 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.
umount(2), path_resolution(7), mount(8), umount(8)
This page is part of release 3.32 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/.
Linux 2010-09-10 MOUNT(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface