umount(8)

NAME

   umount - unmount file systems

SYNOPSIS

   umount -a [-dflnrv] [-t fstype] [-O option...]

   umount [-dflnrv] {directory|device}...

   umount -h|-V

DESCRIPTION

   The  umount command detaches the mentioned file system(s) 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   lives may also work, but is obsolete, mainly because it  will  fail  in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 filesystems described in /proc/self/mountinfo (or  in
          deprecated  /etc/mtab)  are  unmounted,  except the proc, devfs,
          devpts, sysfs, rpc_pipefs and nfsd filesystems. This list of the
          filesystems may be replaced by --types umount option.

   -A, --all-targets
          Unmount  all  mountpoints  in  the  current  namespace  for  the
          specified filesystem.  The filesystem can be specified by one of
          the  mountpoints  or the device name (or UUID, etc.).  When this
          option is used together with --recursive, then all nested mounts
          within the filesystem are recursively unmounted.  This option is
          only supported on  systems  where  /etc/mtab  is  a  symlink  to
          /proc/mounts.

   -c, --no-canonicalize
          Do  not  canonicalize paths.  For more details about this option
          see the mount(8) man page.  Note that umount does not pass  this
          option to the /sbin/umount.type helpers.

   -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
          or   umount   helper  execution;  this  'fakes'  unmounting  the
          filesystem.   It  can  be  used  to  remove  entries  from   the
          deprecated  /etc/mtab  that  were  unmounted earlier with the -n
          option.

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

          Note  that  this  option  does not guarantee that umount command
          does not hang.  It's strongly recommended to use absolute  paths
          without symlinks to avoid unwanted readlink and stat syscalls on
          unreachable NFS in umount.

   -i, --internal-only
          Do not  call  the  /sbin/umount.filesystem  helper  even  if  it
          exists.   By  default  such  a  helper  program  is called if it
          exists.

   -l, --lazy
          Lazy unmount.  Detach the filesystem  from  the  file  hierarchy
          now,  and  clean up all references to this filesystem as soon as
          it is not busy anymore.  (Requires kernel 2.4.11 or later.)

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

   -O, --test-opts option...
          Unmount only the filesystems that have the specified option  set
          in  /etc/fstab.   More  than  one  option  may be specified in a
          comma-separated list.  Each option can be prefixed  with  no  to
          indicate that no action should be taken for this option.

   -R, --recursive
          Recursively  unmount  each  specified  directory.  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; a recursive unmount by device
          name (or UUID) is unsupported.

   -r, --read-only
          When an unmount fails, try to remount the filesystem read-only.

   -t, --types type...
          Indicate that the actions should only be taken on filesystems of
          the  specified  type.   More than one type may be specified in a
          comma-separated list.  The  list  of  filesystem  types  can  be
          prefixed  with no to indicate that no action should be taken for
          all of the mentioned types.   Note that umount reads information
          about   mounted   filesystems  from  kernel  (/proc/mounts)  and
          filesystem names may be different than filesystem names used  in
          the /etc/fstab (e.g. "nfs4" vs. "nfs").

   -v, --verbose
          Verbose mode.

   -V, --version
          Display version information and exit.

   -h, --help
          Display help text and exit.

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.

EXTERNAL HELPERS

   The syntax of external unmount helpers is:

          umount.suffix {directory|device} [-flnrv] [-t type.subtype]

   where  suffix  is  the filesystem type (or the value from a uhelper= or
   helper= marker in the mtab file).   The  -t  option  can  be  used  for
   filesystems that have subtype support.  For example:

          umount.fuse -t fuse.sshfs

   A  uhelper=something  marker  (unprivileged  helper)  can appear in the
   /etc/mtab file when ordinary  users  need  to  be  able  to  unmount  a
   mountpoint  that is not defined in /etc/fstab (for example for a device
   that was mounted by udisks(1)).

   A helper=type marker  in  the  mtab  file  will  redirect  all  unmount
   requests to the /sbin/umount.type helper independently of UID.

   Note  that  /etc/mtab  is  currently deprecated and helper= and another
   userspace mount options are maintained by libmount.

FILES

   /etc/mtab
          table of mounted filesystems (deprecated and usually replaced by
          symlink to /proc/mounts)

   /etc/fstab
          table of known filesystems

   /proc/self/mountinfo
          table of mounted filesystems generated by kernel.

ENVIRONMENT

   LIBMOUNT_FSTAB=<path>
          overrides  the  default  location of the fstab file (ignored for
          suid)

   LIBMOUNT_MTAB=<path>
          overrides the default location of the  mtab  file  (ignored  for
          suid)

   LIBMOUNT_DEBUG=all
          enables libmount 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/.

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