attaches the file system specified by
(which is often a device name, but can also be a directory name
or a dummy) to the directory specified by
Appropriate privilege (Linux: the
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
argument supported by the kernel are listed in
(like "minix", "ext2", "ext3", "jfs", "xfs", "reiserfs",
"msdos", "proc", "nfs", "iso9660" etc.).
Further types may become available when the appropriate modules
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
arguments are ignored.
Up until Linux 2.6.26,
was also ignored
(the bind mount has the same mount options as
the underlying mount point).
Since Linux 2.6.26, the
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
Permit mandatory locking on files in this file system.
(Mandatory locking must still be enabled on a per-file basis,
as described in
Move a subtree.
specifies an existing mount point and
specifies the new location.
The move is atomic: at no point is the subtree unmounted.
filesystemtype, mountflags, and data
arguments are ignored.
Do not update access times for (all types of) files on this file system.
Do not allow access to devices (special files) on this file system.
Do not update access times for directories on this file system.
This flag provides a subset of the functionality provided by
Do not allow programs to be executed from this file system.
Do not honor set-user-ID and set-group-ID bits when executing
programs from this file system.
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
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
was specified), and the
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.
Remount an existing mount.
This allows you to change the
of an existing mount without having to unmount and remount the file system.
should be the same values specified in the initial
can be changed:
before kernel 2.6.16, the following could also be changed:
and, additionally, before kernel 2.4.10, the following could also be changed:
MS_SILENT (since Linux 2.6.17)
Suppress the display of certain
warning messages in the kernel log.
This flag supersedes the misnamed and obsolete
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
Make writes on this file system synchronous (as though
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,
are also settable on a per-mount-point basis.
flag is also settable on a per-mount-point basis.
argument is interpreted by the different file systems.
Typically it is a string of comma-separated options
understood by this file system.
for details of the options available for each filesystem type.
On success, zero is returned.
On error, -1 is returned, and
is set appropriately.
The error values given below result from filesystem type independent
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.
Or, mounting a read-only filesystem was attempted without giving the
Or, the block device
is located on a filesystem mounted with the
is already mounted.
Or, it cannot be remounted read-only,
because it still holds files open for writing.
Or, it cannot be mounted on
is still busy (it is the working directory of some task,
the mount point of another device, has open files, etc.).
One of the pointer arguments points outside the user address space.
had an invalid superblock.
Or, a remount
was attempted, but
was not already mounted on
Or, a move
was attempted, but
was not a mount point, or was '/'.
Too many links encountered during pathname resolution.
Or, a move was attempted, while
is a descendant of
(In case no block device is required:)
Table of dummy devices is full.
A pathname was longer than
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.
is not a block device (and a device was required).
or a prefix of
is not a directory.
The major number of the block device
is out of range.
The caller does not have the required privileges.
The definitions of
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.
flag was renamed
when a different
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
would fail with
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
shares its parent's mount namespace;
the mount namespace is preserved across an
A process can obtain a private mount namespace if:
it was created using the
in which case its new namespace is initialized to be a
of the namespace of the process that called
or it calls
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.
file exposes the list of mount points in the mount
namespace of the process with the specified ID; see