UMOUNT(8) System Administration UMOUNT(8)
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lives may also work, but is obsolete, mainly because it will fail in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 descrip-
tion bellow.
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 speci-
fied 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 avail-
able). 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 filesys-
tem. 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 net-
work partition. Remounts of the share will not be possible.
-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 pre-
fixed 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 los-
etup(8) output for more details), otherwise it's necessary to use the
option --detach-loop or call losetup -d <device>. The autoclear fea-
ture 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 mount-
point 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/>.
util-linux July 2014 UMOUNT(8)
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