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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       device  on  which  the file system lives may also work, but is obsolete, mainly because it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 prob-
       lem.

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 specified 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 hierarchy now, and cleanup
              all references to the filesystem as soon as it is not busy anymore.  (Requires ker-
              nel 2.4.11 or later.)

       -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 sepa-
              rated  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 determined 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 prefixed 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  losetup(8)  output  for
       more  details),  otherwise it's necessary to use the option  --detach-loop or call losetup
       -d <device>. The autoclear feature 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 subtypes 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>  inde-
       pendently 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)

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