UMOUNT(8)		     System Administration		     UMOUNT(8)



NAME
       umount - unmount file systems

SYNOPSIS
       umount [-hV]

       umount -a [-dflnrv] [-t vfstype] [-O options]
       umount [-dflnrv] {dir|device}...

DESCRIPTION
       The  umount command detaches the file system(s) mentioned from the file
       hierarchy.  A file system is specified by giving the directory where it
       has  been  mounted.  Giving the special device on which the file system
       lives may also work, but is obsolete, mainly because it	will  fail  in
       case this device was mounted on more than one directory.

       Note  that  a  file  system cannot be unmounted when it is 'busy' - for
       example, when there are open files on it, or when some process has  its
       working	directory  there,  or  when  a swap file on it is in use.  The
       offending process could even be umount itself - it opens libc, and libc
       in  its	turn may open for example locale files.	 A lazy unmount avoids
       this problem, but it may introduce another issues. See --lazy  descrip-
       tion bellow.

OPTIONS
       -a, --all
	      All  of  the  file systems described in /etc/mtab are unmounted.
	      (With umount version 2.7 and later: the proc filesystem  is  not
	      unmounted.)

       -A, --all-targets
	      Unmount  all mountpoints in the current namespace for the speci-
	      fied filesystem.	The filesystem could be specified  by  one  of
	      the  mountpoints	or  device  name  (or UUID, etc.). This option
	      could be used together with --recursive then all	nested	mounts
	      within the filesystem are recursively unmounted.

       -c, --no-canonicalize
	      Do  not  canonicalize paths.  For more details about this option
	      see the mount(8) man page.

       -d, --detach-loop
	      When the unmounted device was a loop device, also free this loop
	      device.  This  option  is unnecessary for devices initialized by
	      mount(8), in this case "autoclear" functionality is  enabled  by
	      default.

       --fake Causes  everything to be done except for the actual system call;
	      this 'fakes' unmounting the  filesystem.	 It  can  be  used  to
	      remove  entries  from /etc/mtab that were unmounted earlier with
	      the -n option.

       -f, --force
	      Force unmount (in case of an unreachable NFS system).  (Requires
	      kernel 2.1.116 or later.)

       -i, --internal-only
	      Do  not  call  the  /sbin/umount.<filesystem>  helper even if it
	      exists.  By default /sbin/umount.<filesystem> helper  is	called
	      if one exists.

       -n, --no-mtab
	      Unmount without writing in /etc/mtab.

       -l, --lazy
	      Lazy unmount.  Detach the filesystem from the filesystem hierar-
	      chy now, and cleanup all references to the filesystem as soon as
	      it is not busy anymore.  (Requires kernel 2.4.11 or later.)

	      A system reboot would be expected in near future if you're going
	      to use this option for network filesystem	 or  local  filesystem
	      with  submounts.	 The  recommended use-case for umount -l is to
	      prevent hangs on shutdown due to an  unreachable	network	 share
	      where a normal umount will hang due to a downed server or a net-
	      work partition. Remounts of the share will not be possible.


       -O, --test-opts options,list
	      Indicate that the actions should only be taken on	 file  systems
	      with  the specified options in /etc/fstab.  More than one option
	      type may be specified in a comma separated  list.	  Each	option
	      can  be  prefixed with no to specify options for which no action
	      should be taken.

       -R, --recursive
	      Recursively unmount each directory specified. Recursion for each
	      directory	 will stop if any unmount operation in the chain fails
	      for any reason. The relationship between mountpoints  is	deter-
	      mined  by	 /proc/self/mountinfo  entries. The filesystem must be
	      specified by mountpoint path, recursive unmount by  device  name
	      (or UUID) is unsupported.

       -r, --read-only
	      In case unmounting fails, try to remount read-only.

       -t, --types vfstype,ext2,ext3
	      Indicate	that  the actions should only be taken on file systems
	      of the specified type.  More than one type may be specified in a
	      comma separated list.  The list of file system types can be pre-
	      fixed with no to specify the  file  system  types	 on  which  no
	      action should be taken.

       -v, --verbose
	      Verbose mode.

       -h, --help
	      Print help message and exit.

       -V, --version
	      Print version and exit.

THE LOOP DEVICE
       The  umount  command  will  automatically detach loop device previously
       initialized by mount(8) command independently of /etc/mtab.

       In this case the device is initialized with "autoclear" flag (see  los-
       etup(8)	output	for more details), otherwise it's necessary to use the
       option  --detach-loop or call losetup -d <device>. The  autoclear  fea-
       ture is supported since Linux 2.6.25.

NOTES
       The syntax of external umount helpers is:

       /sbin/umount.<suffix> {dir|device} [-nlfvr] [-t type.subtype]

       where  the  <suffix>  is	 filesystem type or a value from "uhelper=" or
       "helper=" mtab option.  The -t option is used for filesystems with sub-
       types support (for example /sbin/mount.fuse -t fuse.sshfs).

       The  uhelper= (unprivileged umount helper) is possible to use when non-
       root user wants to umount a mountpoint which  is	 not  defined  in  the
       /etc/fstab file (e.g. devices mounted by udisk).

       The   helper=  mount  option  redirects	all  umount  requests  to  the
       /sbin/umount.<helper> independently on UID.

FILES
       /etc/mtab table of mounted file systems

ENVIRONMENT
       LIBMOUNT_FSTAB=<path>
	      overrides the default location of the fstab file

       LIBMOUNT_MTAB=<path>
	      overrides the default location of the mtab file

       LIBMOUNT_DEBUG=0xffff
	      enables debug output

SEE ALSO
       umount(2), mount(8), losetup(8)

HISTORY
       A umount command appeared in Version 6 AT&T UNIX.

AVAILABILITY
       The umount command is part of the util-linux package and	 is  available
       from  Linux  Kernel Archive <ftp://ftp.kernel.org/pub/linux/utils/util-
       linux/>.



util-linux			  August 2012			     UMOUNT(8)