NAME
mount, umount, umount2 - mount and unmount filesystems
SYNOPSIS
#include <sys/mount.h>
I int mount(const char * source , const char * target ,
I const char * filesystemtype , unsigned long mountflags ,
I const void * data );
I int umount(const char * target );
I int umount2(const char * target , int flags );
DESCRIPTION
R 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
R target .
R umount ()
and
R umount2 ()
remove the attachment of the (topmost) filesystem mounted on
R 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
R 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
R 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
R filesystemtype , mountflags , and data
arguments are ignored.
R 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(8).)
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
R 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.
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.
R 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_REMOUNT
Remount an existing mount.
This is 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
R mount ()
call;
filesystemtype
is ignored.
The following
mountflags
can be changed:
R MS_RDONLY ,
R MS_SYNCHRONOUS ,
R MS_MANDLOCK ;
before kernel 2.6.16, the following could also be changed:
R MS_NOATIME
and
R MS_NODIRATIME ;
and, additionally, before kernel 2.4, the following could also be changed:
R MS_NOSUID ,
R MS_NODEV ,
R MS_NOEXEC .
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 onwards, the
R 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
R 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
R umount2 ()
system call, which, like
R umount (),
unmounts a target, but allows additional
flags
controlling the behavior of the operation:
R MNT_FORCE (since Linux 2.1.116)
Force unmount even if busy.
This can cause data loss.
(Only for NFS mounts.)
R 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.
R 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
R umount2 ()
with this flag fails with the error
R 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
R umount2 ()
call specifying
MNT_EXPIRE
unmounts an expired mount point.
This flag cannot be specified with either
MNT_FORCE
or
R MNT_DETACH .
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
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.
EACCES
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.
EAGAIN
A call to
R umount2 ()
specifying
MNT_EXPIRE
successfully marked an unbusy file system as expired.
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.).
Or, it could not be unmounted because it is busy.
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
R 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,
R umount2 ()
was called with
MNT_EXPIRE
and either
MNT_DETACH
or
R MNT_FORCE .
ELOOP
Too many link encountered during pathname resolution.
Or, a move was attempted, while
target
is a descendant of
R source .
EMFILE
(In case no block device is required:)
Table of dummy devices is full.
ENAMETOOLONG
A pathname was longer than
R 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
The second argument, or a prefix of the first argument, 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.
CONFORMING TO
These functions are Linux specific and should not be used in
programs intended to be portable.
NOTES
Linux Notes
The original
R 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
R MS_SYNC
flag was renamed
R MS_SYNCHRONOUS
in 1.1.69
when a different
R 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
R EPERM .
Since Linux 2.4 the set-user-ID and set-group-ID bits are
just silently ignored in this case.
SEE ALSO