mount.2

MOUNT(2)                   Linux Programmer's Manual                  MOUNT(2)



NAME
       mount, umount - mount and unmount filesystems

SYNOPSIS
       #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);

DESCRIPTION
       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(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 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 honour 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 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 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_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 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
       behaviour 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.

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(2).)  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 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 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.

       ELOOP  Too many link 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
              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.

HISTORY
       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.

SEE ALSO
       path_resolution(2), mount(8), umount(8)



Linux 2.6.12                      2004-05-18                          MOUNT(2)