UMOUNT

Section: System Administration (8)
Updated: July 2014
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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 Giving the special device on which the file system lives may also work, but is obsolete, mainly because it will fail in case this device was mounted on more than one directory.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 /etc/mtab are unmounted, except the proc filesystem.
-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. 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.
--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 an 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 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. (Requires kernel 2.4.11 or later.)
-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.
-v, --verbose: Verbose mode.
-V, --version: Display version information and exit.
-h, --help: Display help text and exit.

LOOP DEVICE

The umount command will free the loop device associated with a mount when it finds the option loop=... in /etc/mtab, or when the -d option was given. Any still associated loop devices can be freed by using losetup -d; see losetup(8).

EXTERNAL HELPERS

The syntax of external unmount helpers is:

/sbin/umount.suffix {directory|device} [-flnrv] [-t type.subtype]

where suffix is the filesystem type or a value from a "uhelper=" or "helper=" mtab option. The -t option can be used for filesystems with subtypes support (for example /sbin/mount.fuse -t fuse.sshfs).

The uhelper= (unprivileged unmount helper) mount option can be used when non-root users need to be able to unmount a mountpoint which is not defined in /etc/fstab (e.g. devices mounted by udisk).

The helper= mount option redirects all unmount requests to the /sbin/umount.type helper independently of UID.

FILES

/etc/mtab: table of mounted filesystems
/etc/fstab: checked when option -O is given

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

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