Provided by: mount_2.31.1-0.4ubuntu3.7_amd64 bug


       umount - unmount file systems


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

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

       umount -h|-V


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       device  on  which  the file system lives may also work, but is obsolete, mainly because it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


       -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

       -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

       -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.


       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.


       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

              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.


              table of mounted  filesystems  (deprecated  and  usually  replaced  by  symlink  to

              table of known filesystems

              table of mounted filesystems generated by kernel.


              overrides the default location of the fstab file (ignored for suid)

              overrides the default location of the mtab file (ignored for suid)

              enables libmount debug output


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


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


       The  umount  command  is part of the util-linux package and is available from Linux Kernel
       Archive ⟨⟩.