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 Giving the special device on which the file system lives may also work, but is obsolete, mainly because it will fail in case this device was mounted on more than one directory.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 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 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 network 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 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> 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/).