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



NAME
       mount, umount, umount2 - mount and unmount file systems

SYNOPSIS
       #include <&lt;sys/mount.h>&gt;

       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 file system 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) file sys-
       tem mounted on target.

       Appropriate privilege (Linux: the CAP_SYS_ADMIN capability) is required
       to mount and unmount 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", "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  &lt;linux/fs.h&gt;  for  libc4  and  libc5  and   in
       &lt;sys/mount.h&gt; 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 visi-
              ble 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 mound 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.
              Since Linux 2.6.2

       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.   (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.
              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.

       MS_REMOUNT
              Remount an existing mount.  This allows you to change the mount-
              flags 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;  filesystem-
              type is ignored.

              The  following mountflags can be changed: MS_RDONLY, MS_SYNCHRO-
              NOUS, MS_MANDLOCK; before kernel  2.6.16,  the  following  could
              also  be  changed:  MS_NOATIME and MS_NODIRATIME; and, addition-
              ally, before kernel 2.4.10, 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.  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 behavior
       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 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_reso-
              lution(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 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.

NOTES
   Linux Notes
       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 &lt;mman.h&gt;.

       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(7), mount(8), umount(8)

COLOPHON
       This  page  is  part of release 3.05 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                             2008-07-17                          MOUNT(2)