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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_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, 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	behav‐
       iour 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)
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