Provided by: mount_2.36.1-7ubuntu2_amd64 bug

NAME

       umount - unmount filesystems

SYNOPSIS

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

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

       umount -h|-V

DESCRIPTION

       The  umount  command  detaches  the  mentioned  filesystem(s)  from the file hierarchy.  A
       filesystem is specified by giving the directory where it has  been  mounted.   Giving  the
       special  device  on  which  the  filesystem  lives  may also work, but is obsolete, mainly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 filesystem 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, but it may introduce other issues. See --lazy description below.

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  mount  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.

              A system reboot would be expected in near future if you're going to use this option
              for  network  filesystem  or local filesystem with submounts.  The recommended use-
              case for umount -l is to prevent hangs on shutdown due to  an  unreachable  network
              share  where  a  normal  umount  will  hang  due  to  a  downed server or a network
              partition. Remounts of the share will not be possible.

       -N, --namespace ns
              Perform umount in the mount namespace specified by ns.  ns is either PID of process
              running in that namespace or special file representing that namespace.

              umount(8)  switches to the namespace when it reads /etc/fstab, writes /etc/mtab (or
              writes to /run/mount) and calls umount(2) system call, otherwise  it  runs  in  the
              original  namespace.   It  means  that  the target mount namespace does not have to
              contain any libraries or other requirements necessary to execute umount(2) command.

              See mount_namespaces(7) for more information.

       -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.

       -q, --quiet
              Suppress "not mounted" error messages.

       -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.

NON-SUPERUSER UMOUNTS

       Normally,  only  the  superuser  can umount filesystems.  However, when fstab contains the
       user option on a line, anybody can umount the corresponding filesystem.  For more  details
       see mount(8) man page.

       Since  version  2.34  the  umount command can be used to perform umount operation also for
       fuse filesystems if kernel mount table contains user's ID.  In this case fstab user= mount
       option is not required.

       Since  version  2.35  umount command does not exit when user permissions are inadequate by
       internal libmount security rules.  It drops suid permissions and continue as regular  non-
       root user.  This can be used to support use-cases where root permissions are not necessary
       (e.g., fuse filesystems, user namespaces, etc).

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] [-N namespace] [-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 other userspace mount  options
       are maintained by libmount.

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

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.

HISTORY

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

SEE ALSO

       umount(2), losetup(8), mount_namespaces(7) mount(8)

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/⟩.