bionic (8) umount.8.gz

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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       system  lives may also work, but is obsolete, mainly because it will fail in case this device was mounted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.  The paths canonicalization is based on stat(2) and readlink(2)  system
              calls.  These system calls may hang in some cases (for example on NFS if server is not available).
              The option has to be used with canonical path to the mount point.

              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).

              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  system
              calls 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.

       -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), losetup(8), mount(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 ⟨https://
       www.kernel.org/pub/linux/utils/util-linux/⟩.