Provided by: mount_2.34-0.1ubuntu9.6_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system lives may also work, but is obsolete, mainly because it will fail in case this device was mounted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, but it may introduce another 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 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 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 namespace does not have to contain any libraries or another requirements necessary
to execute umount(2) command.
See 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.
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 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/⟩.