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umount


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       lives may also work, but is obsolete, mainly because it  will  fail  in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.


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.)

              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-
              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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