• NAME
  
  umount, umount2 - unmount file system
• 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) file system mounted on
  target .
  
  
  
  
  Appropriate privilege (Linux: the
  CAP_SYS_ADMIN capability) is required to unmount file systems.
  
  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 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.
  

  EAGAIN

  A call to
  umount2 ()
  specifying
  MNT_EXPIRE successfully marked an unbusy file system 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.
  Or,
  umount2 ()
  was called with
  MNT_EXPIRE and either
  MNT_DETACH or
  MNT_FORCE .
  

  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.
  

• 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 3.19 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/.
  

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