Ubuntu Manpage: umount - unmount file systems

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

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       device  on  which  the file system lives may also work, but is obsolete, mainly because it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

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/⟩.