UMOUNT(8) System Administration UMOUNT(8)
NAME
umount - unmount file systems
SYNOPSIS
umount [-hV]
umount -a [-dflnrv] [-t vfstype] [-O options]
umount [-dflnrv] {dir|device}...
DESCRIPTION
The umount command detaches the file system(s) mentioned 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lives may also work, but is obsolete, mainly because it will fail in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 file systems described in /etc/mtab are unmounted.
(With umount version 2.7 and later: the proc filesystem is not
unmounted.)
-A, --all-targets
Unmount all mountpoints in the current namespace for the speci-
fied filesystem. The filesystem could be specified by one of
the mountpoints or device name (or UUID, etc.). This option
could be used together with --recursive then all nested mounts
within the filesystem are recursively unmounted.
-c, --no-canonicalize
Do not canonicalize paths. For more details about this option
see the mount(8) man page.
-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;
this 'fakes' unmounting the filesystem. It can be used to
remove entries from /etc/mtab that were unmounted earlier with
the -n option.
-f, --force
Force unmount (in case of an unreachable NFS system). (Requires
kernel 2.1.116 or later.)
-i, --internal-only
Do not call the /sbin/umount.<filesystem> helper even if it
exists. By default /sbin/umount.<filesystem> helper is called
if one exists.
-n, --no-mtab
Unmount without writing in /etc/mtab.
-l, --lazy
Lazy unmount. Detach the filesystem from the filesystem hierar-
chy now, and cleanup all references to the filesystem as soon as
it is not busy anymore. (Requires kernel 2.4.11 or later.)
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.
-O, --test-opts options,list
Indicate that the actions should only be taken on file systems
with the specified options in /etc/fstab. More than one option
type may be specified in a comma separated list. Each option
can be prefixed with no to specify options for which no action
should be taken.
-R, --recursive
Recursively unmount each directory specified. Recursion for each
directory will stop if any unmount operation in the chain fails
for any reason. The relationship between mountpoints is deter-
mined by /proc/self/mountinfo entries. The filesystem must be
specified by mountpoint path, recursive unmount by device name
(or UUID) is unsupported.
-r, --read-only
In case unmounting fails, try to remount read-only.
-t, --types vfstype,ext2,ext3
Indicate that the actions should only be taken on file systems
of the specified type. More than one type may be specified in a
comma separated list. The list of file system types can be pre-
fixed with no to specify the file system types on which no
action should be taken.
-v, --verbose
Verbose mode.
-h, --help
Print help message and exit.
-V, --version
Print version and exit.
THE 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.
NOTES
The syntax of external umount helpers is:
/sbin/umount.<suffix> {dir|device} [-nlfvr] [-t type.subtype]
where the <suffix> is filesystem type or a value from "uhelper=" or
"helper=" mtab option. The -t option is used for filesystems with sub-
types support (for example /sbin/mount.fuse -t fuse.sshfs).
The uhelper= (unprivileged umount helper) is possible to use when non-
root user wants to umount a mountpoint which is not defined in the
/etc/fstab file (e.g. devices mounted by udisk).
The helper= mount option redirects all umount requests to the
/sbin/umount.<helper> independently on UID.
FILES
/etc/mtab table of mounted file systems
ENVIRONMENT
LIBMOUNT_FSTAB=<path>
overrides the default location of the fstab file
LIBMOUNT_MTAB=<path>
overrides the default location of the mtab file
LIBMOUNT_DEBUG=0xffff
enables debug output
SEE ALSO
umount(2), mount(8), losetup(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 <ftp://ftp.kernel.org/pub/linux/utils/util-
linux/>.
util-linux August 2012 UMOUNT(8)
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