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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device on which the file system lives may also work, but is obsolete, mainly because it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 prob-
lem, but it may introduce another issues. See --lazy description 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 specified 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 hierarchy now, and cleanup
all references to the filesystem as soon as it is not busy anymore. (Requires ker-
nel 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 network parti-
tion. 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 sepa-
rated 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 determined 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 prefixed 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 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.
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 subtypes 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> inde-
pendently 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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