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

NAME
       umount, umount2 - unmount filesystem

SYNOPSIS
       #include	<sys/mount.h>

       int umount(const	char *target);

       int umount2(const char *target, int flags);

DESCRIPTION
       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 unmount filesystems.

       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  ex-
	      pired.   The mount point remains expired as long as it isn't ac-
	      cessed 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.

       UMOUNT_NOFOLLOW (since Linux 2.6.34)
	      Don't dereference	target if it is	a symbolic  link.   This  flag
	      allows  security problems	to be avoided in set-user-ID-root pro-
	      grams that allow unprivileged users to unmount filesystems.

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 Linux kernel source code for details.

       EAGAIN A	call to	umount2() specifying MNT_EXPIRE	successfully marked an
	      unbusy filesystem	as expired.

       EBUSY  target could not be unmounted because it is busy.

       EFAULT target points outside the	user address space.

       EINVAL target is	not a mount point.

       EINVAL umount2()	was called with	MNT_EXPIRE and	either	MNT_DETACH  or
	      MNT_FORCE.

       EINVAL (since Linux 2.6.34)
	      umount2()	was called with	an invalid flag	value in flags.

       ENAMETOOLONG
	      A	pathname was longer than MAXPATHLEN.

       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.

       EPERM  The caller does not have the required privileges.

VERSIONS
       MNT_DETACH and MNT_EXPIRE are available in glibc	since version 2.11.

CONFORMING TO
       These functions are Linux-specific and should not be used  in  programs
       intended	to be portable.

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).

SEE ALSO
       mount(2), path_resolution(7), mount(8), umount(8)

COLOPHON
       This page is part of release 3.74 of the	Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       http://www.kernel.org/doc/man-pages/.

Linux				  2014-02-26			     UMOUNT(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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