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 direc-
       tory specified by target.

       umount()  and umount2() remove the attachment of the (topmost) filesys-
       tem 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.  (Manda-
              tory 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 sys-
              tem.

       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_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_SYN-
              CHRONOUS, MS_MANDLOCK; before kernel 2.6.16, the following could
              also be changed: MS_NOATIME and  MS_NODIRATIME;  and,  addition-
              ally,  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  data argument is interpreted by the different file systems.  Typi-
       cally 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.  (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  cur-
              rently  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_resolu-
              tion(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 work-
              ing 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)